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File in VSC is not opening [duplicate]

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How do I read every line of a file in Python and store each line as an element in a list?
I want to read the file line by line and append each line to the end of the list.

This code will read the entire file into memory and remove all whitespace characters (newlines and spaces) from the end of each line:
with open(filename) as file:
lines = [line.rstrip() for line in file]
If you're working with a large file, then you should instead read and process it line-by-line:
with open(filename) as file:
for line in file:
print(line.rstrip())
In Python 3.8 and up you can use a while loop with the walrus operator like so:
with open(filename) as file:
while (line := file.readline().rstrip()):
print(line)
Depending on what you plan to do with your file and how it was encoded, you may also want to manually set the access mode and character encoding:
with open(filename, 'r', encoding='UTF-8') as file:
while (line := file.readline().rstrip()):
print(line)

See Input and Ouput:
with open('filename') as f:
lines = f.readlines()
or with stripping the newline character:
with open('filename') as f:
lines = [line.rstrip('\n') for line in f]

This is more explicit than necessary, but does what you want.
with open("file.txt") as file_in:
lines = []
for line in file_in:
lines.append(line)

This will yield an "array" of lines from the file.
lines = tuple(open(filename, 'r'))
open returns a file which can be iterated over. When you iterate over a file, you get the lines from that file. tuple can take an iterator and instantiate a tuple instance for you from the iterator that you give it. lines is a tuple created from the lines of the file.

According to Python's Methods of File Objects, the simplest way to convert a text file into a list is:
with open('file.txt') as f:
my_list = list(f)
# my_list = [x.rstrip() for x in f] # remove line breaks
Demo
If you just need to iterate over the text file lines, you can use:
with open('file.txt') as f:
for line in f:
...
Old answer:
Using with and readlines() :
with open('file.txt') as f:
lines = f.readlines()
If you don't care about closing the file, this one-liner will work:
lines = open('file.txt').readlines()
The traditional way:
f = open('file.txt') # Open file on read mode
lines = f.read().splitlines() # List with stripped line-breaks
f.close() # Close file

If you want the \n included:
with open(fname) as f:
content = f.readlines()
If you do not want \n included:
with open(fname) as f:
content = f.read().splitlines()

You could simply do the following, as has been suggested:
with open('/your/path/file') as f:
my_lines = f.readlines()
Note that this approach has 2 downsides:
1) You store all the lines in memory. In the general case, this is a very bad idea. The file could be very large, and you could run out of memory. Even if it's not large, it is simply a waste of memory.
2) This does not allow processing of each line as you read them. So if you process your lines after this, it is not efficient (requires two passes rather than one).
A better approach for the general case would be the following:
with open('/your/path/file') as f:
for line in f:
process(line)
Where you define your process function any way you want. For example:
def process(line):
if 'save the world' in line.lower():
superman.save_the_world()
(The implementation of the Superman class is left as an exercise for you).
This will work nicely for any file size and you go through your file in just 1 pass. This is typically how generic parsers will work.

Having a Text file content:
line 1
line 2
line 3
We can use this Python script in the same directory of the txt above
>>> with open("myfile.txt", encoding="utf-8") as file:
... x = [l.rstrip("\n") for l in file]
>>> x
['line 1','line 2','line 3']
Using append:
x = []
with open("myfile.txt") as file:
for l in file:
x.append(l.strip())
Or:
>>> x = open("myfile.txt").read().splitlines()
>>> x
['line 1', 'line 2', 'line 3']
Or:
>>> x = open("myfile.txt").readlines()
>>> x
['linea 1\n', 'line 2\n', 'line 3\n']
Or:
def print_output(lines_in_textfile):
print("lines_in_textfile =", lines_in_textfile)
y = [x.rstrip() for x in open("001.txt")]
print_output(y)
with open('001.txt', 'r', encoding='utf-8') as file:
file = file.read().splitlines()
print_output(file)
with open('001.txt', 'r', encoding='utf-8') as file:
file = [x.rstrip("\n") for x in file]
print_output(file)
output:
lines_in_textfile = ['line 1', 'line 2', 'line 3']
lines_in_textfile = ['line 1', 'line 2', 'line 3']
lines_in_textfile = ['line 1', 'line 2', 'line 3']

Introduced in Python 3.4, pathlib has a really convenient method for reading in text from files, as follows:
from pathlib import Path
p = Path('my_text_file')
lines = p.read_text().splitlines()
(The splitlines call is what turns it from a string containing the whole contents of the file to a list of lines in the file.)
pathlib has a lot of handy conveniences in it. read_text is nice and concise, and you don't have to worry about opening and closing the file. If all you need to do with the file is read it all in in one go, it's a good choice.

To read a file into a list you need to do three things:
Open the file
Read the file
Store the contents as list
Fortunately Python makes it very easy to do these things so the shortest way to read a file into a list is:
lst = list(open(filename))
However I'll add some more explanation.
Opening the file
I assume that you want to open a specific file and you don't deal directly with a file-handle (or a file-like-handle). The most commonly used function to open a file in Python is open, it takes one mandatory argument and two optional ones in Python 2.7:
Filename
Mode
Buffering (I'll ignore this argument in this answer)
The filename should be a string that represents the path to the file. For example:
open('afile') # opens the file named afile in the current working directory
open('adir/afile') # relative path (relative to the current working directory)
open('C:/users/aname/afile') # absolute path (windows)
open('/usr/local/afile') # absolute path (linux)
Note that the file extension needs to be specified. This is especially important for Windows users because file extensions like .txt or .doc, etc. are hidden by default when viewed in the explorer.
The second argument is the mode, it's r by default which means "read-only". That's exactly what you need in your case.
But in case you actually want to create a file and/or write to a file you'll need a different argument here. There is an excellent answer if you want an overview.
For reading a file you can omit the mode or pass it in explicitly:
open(filename)
open(filename, 'r')
Both will open the file in read-only mode. In case you want to read in a binary file on Windows you need to use the mode rb:
open(filename, 'rb')
On other platforms the 'b' (binary mode) is simply ignored.
Now that I've shown how to open the file, let's talk about the fact that you always need to close it again. Otherwise it will keep an open file-handle to the file until the process exits (or Python garbages the file-handle).
While you could use:
f = open(filename)
# ... do stuff with f
f.close()
That will fail to close the file when something between open and close throws an exception. You could avoid that by using a try and finally:
f = open(filename)
# nothing in between!
try:
# do stuff with f
finally:
f.close()
However Python provides context managers that have a prettier syntax (but for open it's almost identical to the try and finally above):
with open(filename) as f:
# do stuff with f
# The file is always closed after the with-scope ends.
The last approach is the recommended approach to open a file in Python!
Reading the file
Okay, you've opened the file, now how to read it?
The open function returns a file object and it supports Pythons iteration protocol. Each iteration will give you a line:
with open(filename) as f:
for line in f:
print(line)
This will print each line of the file. Note however that each line will contain a newline character \n at the end (you might want to check if your Python is built with universal newlines support - otherwise you could also have \r\n on Windows or \r on Mac as newlines). If you don't want that you can could simply remove the last character (or the last two characters on Windows):
with open(filename) as f:
for line in f:
print(line[:-1])
But the last line doesn't necessarily has a trailing newline, so one shouldn't use that. One could check if it ends with a trailing newline and if so remove it:
with open(filename) as f:
for line in f:
if line.endswith('\n'):
line = line[:-1]
print(line)
But you could simply remove all whitespaces (including the \n character) from the end of the string, this will also remove all other trailing whitespaces so you have to be careful if these are important:
with open(filename) as f:
for line in f:
print(f.rstrip())
However if the lines end with \r\n (Windows "newlines") that .rstrip() will also take care of the \r!
Store the contents as list
Now that you know how to open the file and read it, it's time to store the contents in a list. The simplest option would be to use the list function:
with open(filename) as f:
lst = list(f)
In case you want to strip the trailing newlines you could use a list comprehension instead:
with open(filename) as f:
lst = [line.rstrip() for line in f]
Or even simpler: The .readlines() method of the file object by default returns a list of the lines:
with open(filename) as f:
lst = f.readlines()
This will also include the trailing newline characters, if you don't want them I would recommend the [line.rstrip() for line in f] approach because it avoids keeping two lists containing all the lines in memory.
There's an additional option to get the desired output, however it's rather "suboptimal": read the complete file in a string and then split on newlines:
with open(filename) as f:
lst = f.read().split('\n')
or:
with open(filename) as f:
lst = f.read().splitlines()
These take care of the trailing newlines automatically because the split character isn't included. However they are not ideal because you keep the file as string and as a list of lines in memory!
Summary
Use with open(...) as f when opening files because you don't need to take care of closing the file yourself and it closes the file even if some exception happens.
file objects support the iteration protocol so reading a file line-by-line is as simple as for line in the_file_object:.
Always browse the documentation for the available functions/classes. Most of the time there's a perfect match for the task or at least one or two good ones. The obvious choice in this case would be readlines() but if you want to process the lines before storing them in the list I would recommend a simple list-comprehension.

Clean and Pythonic Way of Reading the Lines of a File Into a List
First and foremost, you should focus on opening your file and reading its contents in an efficient and pythonic way. Here is an example of the way I personally DO NOT prefer:
infile = open('my_file.txt', 'r') # Open the file for reading.
data = infile.read() # Read the contents of the file.
infile.close() # Close the file since we're done using it.
Instead, I prefer the below method of opening files for both reading and writing as it
is very clean, and does not require an extra step of closing the file
once you are done using it. In the statement below, we're opening the file
for reading, and assigning it to the variable 'infile.' Once the code within
this statement has finished running, the file will be automatically closed.
# Open the file for reading.
with open('my_file.txt', 'r') as infile:
data = infile.read() # Read the contents of the file into memory.
Now we need to focus on bringing this data into a Python List because they are iterable, efficient, and flexible. In your case, the desired goal is to bring each line of the text file into a separate element. To accomplish this, we will use the splitlines() method as follows:
# Return a list of the lines, breaking at line boundaries.
my_list = data.splitlines()
The Final Product:
# Open the file for reading.
with open('my_file.txt', 'r') as infile:
data = infile.read() # Read the contents of the file into memory.
# Return a list of the lines, breaking at line boundaries.
my_list = data.splitlines()
Testing Our Code:
Contents of the text file:
A fost odatã ca-n povesti,
A fost ca niciodatã,
Din rude mãri împãrãtesti,
O prea frumoasã fatã.
Print statements for testing purposes:
print my_list # Print the list.
# Print each line in the list.
for line in my_list:
print line
# Print the fourth element in this list.
print my_list[3]
Output (different-looking because of unicode characters):
['A fost odat\xc3\xa3 ca-n povesti,', 'A fost ca niciodat\xc3\xa3,',
'Din rude m\xc3\xa3ri \xc3\xaemp\xc3\xa3r\xc3\xa3testi,', 'O prea
frumoas\xc3\xa3 fat\xc3\xa3.']
A fost odatã ca-n povesti, A fost ca niciodatã, Din rude mãri
împãrãtesti, O prea frumoasã fatã.
O prea frumoasã fatã.

Here's one more option by using list comprehensions on files;
lines = [line.rstrip() for line in open('file.txt')]
This should be more efficient way as the most of the work is done inside the Python interpreter.

f = open("your_file.txt",'r')
out = f.readlines() # will append in the list out
Now variable out is a list (array) of what you want. You could either do:
for line in out:
print (line)
Or:
for line in f:
print (line)
You'll get the same results.

Another option is numpy.genfromtxt, for example:
import numpy as np
data = np.genfromtxt("yourfile.dat",delimiter="\n")
This will make data a NumPy array with as many rows as are in your file.

Read and write text files with Python 2 and Python 3; it works with Unicode
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# Define data
lines = [' A first string ',
'A Unicode sample: €',
'German: äöüß']
# Write text file
with open('file.txt', 'w') as fp:
fp.write('\n'.join(lines))
# Read text file
with open('file.txt', 'r') as fp:
read_lines = fp.readlines()
read_lines = [line.rstrip('\n') for line in read_lines]
print(lines == read_lines)
Things to notice:
with is a so-called context manager. It makes sure that the opened file is closed again.
All solutions here which simply make .strip() or .rstrip() will fail to reproduce the lines as they also strip the white space.
Common file endings
.txt
More advanced file writing/reading
CSV: Super simple format (read & write)
JSON: Nice for writing human-readable data; VERY commonly used (read & write)
YAML: YAML is a superset of JSON, but easier to read (read & write, comparison of JSON and YAML)
pickle: A Python serialization format (read & write)
MessagePack (Python package): More compact representation (read & write)
HDF5 (Python package): Nice for matrices (read & write)
XML: exists too *sigh* (read & write)
For your application, the following might be important:
Support by other programming languages
Reading/writing performance
Compactness (file size)
See also: Comparison of data serialization formats
In case you are rather looking for a way to make configuration files, you might want to read my short article Configuration files in Python.

If you'd like to read a file from the command line or from stdin, you can also use the fileinput module:
# reader.py
import fileinput
content = []
for line in fileinput.input():
content.append(line.strip())
fileinput.close()
Pass files to it like so:
$ python reader.py textfile.txt
Read more here: http://docs.python.org/2/library/fileinput.html

The simplest way to do it
A simple way is to:
Read the whole file as a string
Split the string line by line
In one line, that would give:
lines = open('C:/path/file.txt').read().splitlines()
However, this is quite inefficient way as this will store 2 versions of the content in memory (probably not a big issue for small files, but still). [Thanks Mark Amery].
There are 2 easier ways:
Using the file as an iterator
lines = list(open('C:/path/file.txt'))
# ... or if you want to have a list without EOL characters
lines = [l.rstrip() for l in open('C:/path/file.txt')]
If you are using Python 3.4 or above, better use pathlib to create a path for your file that you could use for other operations in your program:
from pathlib import Path
file_path = Path("C:/path/file.txt")
lines = file_path.read_text().split_lines()
# ... or ...
lines = [l.rstrip() for l in file_path.open()]

Just use the splitlines() functions. Here is an example.
inp = "file.txt"
data = open(inp)
dat = data.read()
lst = dat.splitlines()
print lst
# print(lst) # for python 3
In the output you will have the list of lines.

If you are faced with a very large / huge file and want to read faster (imagine you are in a TopCoder or HackerRank coding competition), you might read a considerably bigger chunk of lines into a memory buffer at one time, rather than just iterate line by line at file level.
buffersize = 2**16
with open(path) as f:
while True:
lines_buffer = f.readlines(buffersize)
if not lines_buffer:
break
for line in lines_buffer:
process(line)

The easiest ways to do that with some additional benefits are:
lines = list(open('filename'))
or
lines = tuple(open('filename'))
or
lines = set(open('filename'))
In the case with set, we must be remembered that we don't have the line order preserved and get rid of the duplicated lines.
Below I added an important supplement from #MarkAmery:
Since you're not calling .close on the file object nor using a with statement, in some Python implementations the file may not get closed after reading and your process will leak an open file handle.
In CPython (the normal Python implementation that most people use), this isn't a problem since the file object will get immediately garbage-collected and this will close the file, but it's nonetheless generally considered best practice to do something like:
with open('filename') as f: lines = list(f)
to ensure that the file gets closed regardless of what Python implementation you're using.

Use this:
import pandas as pd
data = pd.read_csv(filename) # You can also add parameters such as header, sep, etc.
array = data.values
data is a dataframe type, and uses values to get ndarray. You can also get a list by using array.tolist().

In case that there are also empty lines in the document I like to read in the content and pass it through filter to prevent empty string elements
with open(myFile, "r") as f:
excludeFileContent = list(filter(None, f.read().splitlines()))

Outline and Summary
With a filename, handling the file from a Path(filename) object, or directly with open(filename) as f, do one of the following:
list(fileinput.input(filename))
using with path.open() as f, call f.readlines()
list(f)
path.read_text().splitlines()
path.read_text().splitlines(keepends=True)
iterate over fileinput.input or f and list.append each line one at a time
pass f to a bound list.extend method
use f in a list comprehension
I explain the use-case for each below.
In Python, how do I read a file line-by-line?
This is an excellent question. First, let's create some sample data:
from pathlib import Path
Path('filename').write_text('foo\nbar\nbaz')
File objects are lazy iterators, so just iterate over it.
filename = 'filename'
with open(filename) as f:
for line in f:
line # do something with the line
Alternatively, if you have multiple files, use fileinput.input, another lazy iterator. With just one file:
import fileinput
for line in fileinput.input(filename):
line # process the line
or for multiple files, pass it a list of filenames:
for line in fileinput.input([filename]*2):
line # process the line
Again, f and fileinput.input above both are/return lazy iterators.
You can only use an iterator one time, so to provide functional code while avoiding verbosity I'll use the slightly more terse fileinput.input(filename) where apropos from here.
In Python, how do I read a file line-by-line into a list?
Ah but you want it in a list for some reason? I'd avoid that if possible. But if you insist... just pass the result of fileinput.input(filename) to list:
list(fileinput.input(filename))
Another direct answer is to call f.readlines, which returns the contents of the file (up to an optional hint number of characters, so you could break this up into multiple lists that way).
You can get to this file object two ways. One way is to pass the filename to the open builtin:
filename = 'filename'
with open(filename) as f:
f.readlines()
or using the new Path object from the pathlib module (which I have become quite fond of, and will use from here on):
from pathlib import Path
path = Path(filename)
with path.open() as f:
f.readlines()
list will also consume the file iterator and return a list - a quite direct method as well:
with path.open() as f:
list(f)
If you don't mind reading the entire text into memory as a single string before splitting it, you can do this as a one-liner with the Path object and the splitlines() string method. By default, splitlines removes the newlines:
path.read_text().splitlines()
If you want to keep the newlines, pass keepends=True:
path.read_text().splitlines(keepends=True)
I want to read the file line by line and append each line to the end of the list.
Now this is a bit silly to ask for, given that we've demonstrated the end result easily with several methods. But you might need to filter or operate on the lines as you make your list, so let's humor this request.
Using list.append would allow you to filter or operate on each line before you append it:
line_list = []
for line in fileinput.input(filename):
line_list.append(line)
line_list
Using list.extend would be a bit more direct, and perhaps useful if you have a preexisting list:
line_list = []
line_list.extend(fileinput.input(filename))
line_list
Or more idiomatically, we could instead use a list comprehension, and map and filter inside it if desirable:
[line for line in fileinput.input(filename)]
Or even more directly, to close the circle, just pass it to list to create a new list directly without operating on the lines:
list(fileinput.input(filename))
Conclusion
You've seen many ways to get lines from a file into a list, but I'd recommend you avoid materializing large quantities of data into a list and instead use Python's lazy iteration to process the data if possible.
That is, prefer fileinput.input or with path.open() as f.

I would try one of the below mentioned methods. The example file that I use has the name dummy.txt. You can find the file here. I presume that the file is in the same directory as the code (you can change fpath to include the proper file name and folder path).
In both the below mentioned examples, the list that you want is given by lst.
1. First method
fpath = 'dummy.txt'
with open(fpath, "r") as f: lst = [line.rstrip('\n \t') for line in f]
print lst
>>>['THIS IS LINE1.', 'THIS IS LINE2.', 'THIS IS LINE3.', 'THIS IS LINE4.']
2. In the second method, one can use csv.reader module from Python Standard Library:
import csv
fpath = 'dummy.txt'
with open(fpath) as csv_file:
csv_reader = csv.reader(csv_file, delimiter=' ')
lst = [row[0] for row in csv_reader]
print lst
>>>['THIS IS LINE1.', 'THIS IS LINE2.', 'THIS IS LINE3.', 'THIS IS LINE4.']
You can use either of the two methods. The time taken for the creation of lst is almost equal for the two methods.

I like to use the following. Reading the lines immediately.
contents = []
for line in open(filepath, 'r').readlines():
contents.append(line.strip())
Or using list comprehension:
contents = [line.strip() for line in open(filepath, 'r').readlines()]

You could also use the loadtxt command in NumPy. This checks for fewer conditions than genfromtxt, so it may be faster.
import numpy
data = numpy.loadtxt(filename, delimiter="\n")

Here is a Python(3) helper library class that I use to simplify file I/O:
import os
# handle files using a callback method, prevents repetition
def _FileIO__file_handler(file_path, mode, callback = lambda f: None):
f = open(file_path, mode)
try:
return callback(f)
except Exception as e:
raise IOError("Failed to %s file" % ["write to", "read from"][mode.lower() in "r rb r+".split(" ")])
finally:
f.close()
class FileIO:
# return the contents of a file
def read(file_path, mode = "r"):
return __file_handler(file_path, mode, lambda rf: rf.read())
# get the lines of a file
def lines(file_path, mode = "r", filter_fn = lambda line: len(line) > 0):
return [line for line in FileIO.read(file_path, mode).strip().split("\n") if filter_fn(line)]
# create or update a file (NOTE: can also be used to replace a file's original content)
def write(file_path, new_content, mode = "w"):
return __file_handler(file_path, mode, lambda wf: wf.write(new_content))
# delete a file (if it exists)
def delete(file_path):
return os.remove() if os.path.isfile(file_path) else None
You would then use the FileIO.lines function, like this:
file_ext_lines = FileIO.lines("./path/to/file.ext"):
for i, line in enumerate(file_ext_lines):
print("Line {}: {}".format(i + 1, line))
Remember that the mode ("r" by default) and filter_fn (checks for empty lines by default) parameters are optional.
You could even remove the read, write and delete methods and just leave the FileIO.lines, or even turn it into a separate method called read_lines.

Command line version
#!/bin/python3
import os
import sys
abspath = os.path.abspath(__file__)
dname = os.path.dirname(abspath)
filename = dname + sys.argv[1]
arr = open(filename).read().split("\n")
print(arr)
Run with:
python3 somefile.py input_file_name.txt

How to take a file name and have it return FASTA data structure? [duplicate]

This question's answers are a community effort. Edit existing answers to improve this post. It is not currently accepting new answers or interactions.
How do I read every line of a file in Python and store each line as an element in a list?
I want to read the file line by line and append each line to the end of the list.

This code will read the entire file into memory and remove all whitespace characters (newlines and spaces) from the end of each line:
with open(filename) as file:
lines = [line.rstrip() for line in file]
If you're working with a large file, then you should instead read and process it line-by-line:
with open(filename) as file:
for line in file:
print(line.rstrip())
In Python 3.8 and up you can use a while loop with the walrus operator like so:
with open(filename) as file:
while (line := file.readline().rstrip()):
print(line)
Depending on what you plan to do with your file and how it was encoded, you may also want to manually set the access mode and character encoding:
with open(filename, 'r', encoding='UTF-8') as file:
while (line := file.readline().rstrip()):
print(line)

See Input and Ouput:
with open('filename') as f:
lines = f.readlines()
or with stripping the newline character:
with open('filename') as f:
lines = [line.rstrip('\n') for line in f]

This is more explicit than necessary, but does what you want.
with open("file.txt") as file_in:
lines = []
for line in file_in:
lines.append(line)

This will yield an "array" of lines from the file.
lines = tuple(open(filename, 'r'))
open returns a file which can be iterated over. When you iterate over a file, you get the lines from that file. tuple can take an iterator and instantiate a tuple instance for you from the iterator that you give it. lines is a tuple created from the lines of the file.

According to Python's Methods of File Objects, the simplest way to convert a text file into a list is:
with open('file.txt') as f:
my_list = list(f)
# my_list = [x.rstrip() for x in f] # remove line breaks
Demo
If you just need to iterate over the text file lines, you can use:
with open('file.txt') as f:
for line in f:
...
Old answer:
Using with and readlines() :
with open('file.txt') as f:
lines = f.readlines()
If you don't care about closing the file, this one-liner will work:
lines = open('file.txt').readlines()
The traditional way:
f = open('file.txt') # Open file on read mode
lines = f.read().splitlines() # List with stripped line-breaks
f.close() # Close file

If you want the \n included:
with open(fname) as f:
content = f.readlines()
If you do not want \n included:
with open(fname) as f:
content = f.read().splitlines()

You could simply do the following, as has been suggested:
with open('/your/path/file') as f:
my_lines = f.readlines()
Note that this approach has 2 downsides:
1) You store all the lines in memory. In the general case, this is a very bad idea. The file could be very large, and you could run out of memory. Even if it's not large, it is simply a waste of memory.
2) This does not allow processing of each line as you read them. So if you process your lines after this, it is not efficient (requires two passes rather than one).
A better approach for the general case would be the following:
with open('/your/path/file') as f:
for line in f:
process(line)
Where you define your process function any way you want. For example:
def process(line):
if 'save the world' in line.lower():
superman.save_the_world()
(The implementation of the Superman class is left as an exercise for you).
This will work nicely for any file size and you go through your file in just 1 pass. This is typically how generic parsers will work.

Having a Text file content:
line 1
line 2
line 3
We can use this Python script in the same directory of the txt above
>>> with open("myfile.txt", encoding="utf-8") as file:
... x = [l.rstrip("\n") for l in file]
>>> x
['line 1','line 2','line 3']
Using append:
x = []
with open("myfile.txt") as file:
for l in file:
x.append(l.strip())
Or:
>>> x = open("myfile.txt").read().splitlines()
>>> x
['line 1', 'line 2', 'line 3']
Or:
>>> x = open("myfile.txt").readlines()
>>> x
['linea 1\n', 'line 2\n', 'line 3\n']
Or:
def print_output(lines_in_textfile):
print("lines_in_textfile =", lines_in_textfile)
y = [x.rstrip() for x in open("001.txt")]
print_output(y)
with open('001.txt', 'r', encoding='utf-8') as file:
file = file.read().splitlines()
print_output(file)
with open('001.txt', 'r', encoding='utf-8') as file:
file = [x.rstrip("\n") for x in file]
print_output(file)
output:
lines_in_textfile = ['line 1', 'line 2', 'line 3']
lines_in_textfile = ['line 1', 'line 2', 'line 3']
lines_in_textfile = ['line 1', 'line 2', 'line 3']

Introduced in Python 3.4, pathlib has a really convenient method for reading in text from files, as follows:
from pathlib import Path
p = Path('my_text_file')
lines = p.read_text().splitlines()
(The splitlines call is what turns it from a string containing the whole contents of the file to a list of lines in the file.)
pathlib has a lot of handy conveniences in it. read_text is nice and concise, and you don't have to worry about opening and closing the file. If all you need to do with the file is read it all in in one go, it's a good choice.

To read a file into a list you need to do three things:
Open the file
Read the file
Store the contents as list
Fortunately Python makes it very easy to do these things so the shortest way to read a file into a list is:
lst = list(open(filename))
However I'll add some more explanation.
Opening the file
I assume that you want to open a specific file and you don't deal directly with a file-handle (or a file-like-handle). The most commonly used function to open a file in Python is open, it takes one mandatory argument and two optional ones in Python 2.7:
Filename
Mode
Buffering (I'll ignore this argument in this answer)
The filename should be a string that represents the path to the file. For example:
open('afile') # opens the file named afile in the current working directory
open('adir/afile') # relative path (relative to the current working directory)
open('C:/users/aname/afile') # absolute path (windows)
open('/usr/local/afile') # absolute path (linux)
Note that the file extension needs to be specified. This is especially important for Windows users because file extensions like .txt or .doc, etc. are hidden by default when viewed in the explorer.
The second argument is the mode, it's r by default which means "read-only". That's exactly what you need in your case.
But in case you actually want to create a file and/or write to a file you'll need a different argument here. There is an excellent answer if you want an overview.
For reading a file you can omit the mode or pass it in explicitly:
open(filename)
open(filename, 'r')
Both will open the file in read-only mode. In case you want to read in a binary file on Windows you need to use the mode rb:
open(filename, 'rb')
On other platforms the 'b' (binary mode) is simply ignored.
Now that I've shown how to open the file, let's talk about the fact that you always need to close it again. Otherwise it will keep an open file-handle to the file until the process exits (or Python garbages the file-handle).
While you could use:
f = open(filename)
# ... do stuff with f
f.close()
That will fail to close the file when something between open and close throws an exception. You could avoid that by using a try and finally:
f = open(filename)
# nothing in between!
try:
# do stuff with f
finally:
f.close()
However Python provides context managers that have a prettier syntax (but for open it's almost identical to the try and finally above):
with open(filename) as f:
# do stuff with f
# The file is always closed after the with-scope ends.
The last approach is the recommended approach to open a file in Python!
Reading the file
Okay, you've opened the file, now how to read it?
The open function returns a file object and it supports Pythons iteration protocol. Each iteration will give you a line:
with open(filename) as f:
for line in f:
print(line)
This will print each line of the file. Note however that each line will contain a newline character \n at the end (you might want to check if your Python is built with universal newlines support - otherwise you could also have \r\n on Windows or \r on Mac as newlines). If you don't want that you can could simply remove the last character (or the last two characters on Windows):
with open(filename) as f:
for line in f:
print(line[:-1])
But the last line doesn't necessarily has a trailing newline, so one shouldn't use that. One could check if it ends with a trailing newline and if so remove it:
with open(filename) as f:
for line in f:
if line.endswith('\n'):
line = line[:-1]
print(line)
But you could simply remove all whitespaces (including the \n character) from the end of the string, this will also remove all other trailing whitespaces so you have to be careful if these are important:
with open(filename) as f:
for line in f:
print(f.rstrip())
However if the lines end with \r\n (Windows "newlines") that .rstrip() will also take care of the \r!
Store the contents as list
Now that you know how to open the file and read it, it's time to store the contents in a list. The simplest option would be to use the list function:
with open(filename) as f:
lst = list(f)
In case you want to strip the trailing newlines you could use a list comprehension instead:
with open(filename) as f:
lst = [line.rstrip() for line in f]
Or even simpler: The .readlines() method of the file object by default returns a list of the lines:
with open(filename) as f:
lst = f.readlines()
This will also include the trailing newline characters, if you don't want them I would recommend the [line.rstrip() for line in f] approach because it avoids keeping two lists containing all the lines in memory.
There's an additional option to get the desired output, however it's rather "suboptimal": read the complete file in a string and then split on newlines:
with open(filename) as f:
lst = f.read().split('\n')
or:
with open(filename) as f:
lst = f.read().splitlines()
These take care of the trailing newlines automatically because the split character isn't included. However they are not ideal because you keep the file as string and as a list of lines in memory!
Summary
Use with open(...) as f when opening files because you don't need to take care of closing the file yourself and it closes the file even if some exception happens.
file objects support the iteration protocol so reading a file line-by-line is as simple as for line in the_file_object:.
Always browse the documentation for the available functions/classes. Most of the time there's a perfect match for the task or at least one or two good ones. The obvious choice in this case would be readlines() but if you want to process the lines before storing them in the list I would recommend a simple list-comprehension.

Clean and Pythonic Way of Reading the Lines of a File Into a List
First and foremost, you should focus on opening your file and reading its contents in an efficient and pythonic way. Here is an example of the way I personally DO NOT prefer:
infile = open('my_file.txt', 'r') # Open the file for reading.
data = infile.read() # Read the contents of the file.
infile.close() # Close the file since we're done using it.
Instead, I prefer the below method of opening files for both reading and writing as it
is very clean, and does not require an extra step of closing the file
once you are done using it. In the statement below, we're opening the file
for reading, and assigning it to the variable 'infile.' Once the code within
this statement has finished running, the file will be automatically closed.
# Open the file for reading.
with open('my_file.txt', 'r') as infile:
data = infile.read() # Read the contents of the file into memory.
Now we need to focus on bringing this data into a Python List because they are iterable, efficient, and flexible. In your case, the desired goal is to bring each line of the text file into a separate element. To accomplish this, we will use the splitlines() method as follows:
# Return a list of the lines, breaking at line boundaries.
my_list = data.splitlines()
The Final Product:
# Open the file for reading.
with open('my_file.txt', 'r') as infile:
data = infile.read() # Read the contents of the file into memory.
# Return a list of the lines, breaking at line boundaries.
my_list = data.splitlines()
Testing Our Code:
Contents of the text file:
A fost odatã ca-n povesti,
A fost ca niciodatã,
Din rude mãri împãrãtesti,
O prea frumoasã fatã.
Print statements for testing purposes:
print my_list # Print the list.
# Print each line in the list.
for line in my_list:
print line
# Print the fourth element in this list.
print my_list[3]
Output (different-looking because of unicode characters):
['A fost odat\xc3\xa3 ca-n povesti,', 'A fost ca niciodat\xc3\xa3,',
'Din rude m\xc3\xa3ri \xc3\xaemp\xc3\xa3r\xc3\xa3testi,', 'O prea
frumoas\xc3\xa3 fat\xc3\xa3.']
A fost odatã ca-n povesti, A fost ca niciodatã, Din rude mãri
împãrãtesti, O prea frumoasã fatã.
O prea frumoasã fatã.

Here's one more option by using list comprehensions on files;
lines = [line.rstrip() for line in open('file.txt')]
This should be more efficient way as the most of the work is done inside the Python interpreter.

f = open("your_file.txt",'r')
out = f.readlines() # will append in the list out
Now variable out is a list (array) of what you want. You could either do:
for line in out:
print (line)
Or:
for line in f:
print (line)
You'll get the same results.

Another option is numpy.genfromtxt, for example:
import numpy as np
data = np.genfromtxt("yourfile.dat",delimiter="\n")
This will make data a NumPy array with as many rows as are in your file.

Read and write text files with Python 2 and Python 3; it works with Unicode
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# Define data
lines = [' A first string ',
'A Unicode sample: €',
'German: äöüß']
# Write text file
with open('file.txt', 'w') as fp:
fp.write('\n'.join(lines))
# Read text file
with open('file.txt', 'r') as fp:
read_lines = fp.readlines()
read_lines = [line.rstrip('\n') for line in read_lines]
print(lines == read_lines)
Things to notice:
with is a so-called context manager. It makes sure that the opened file is closed again.
All solutions here which simply make .strip() or .rstrip() will fail to reproduce the lines as they also strip the white space.
Common file endings
.txt
More advanced file writing/reading
CSV: Super simple format (read & write)
JSON: Nice for writing human-readable data; VERY commonly used (read & write)
YAML: YAML is a superset of JSON, but easier to read (read & write, comparison of JSON and YAML)
pickle: A Python serialization format (read & write)
MessagePack (Python package): More compact representation (read & write)
HDF5 (Python package): Nice for matrices (read & write)
XML: exists too *sigh* (read & write)
For your application, the following might be important:
Support by other programming languages
Reading/writing performance
Compactness (file size)
See also: Comparison of data serialization formats
In case you are rather looking for a way to make configuration files, you might want to read my short article Configuration files in Python.

If you'd like to read a file from the command line or from stdin, you can also use the fileinput module:
# reader.py
import fileinput
content = []
for line in fileinput.input():
content.append(line.strip())
fileinput.close()
Pass files to it like so:
$ python reader.py textfile.txt
Read more here: http://docs.python.org/2/library/fileinput.html

The simplest way to do it
A simple way is to:
Read the whole file as a string
Split the string line by line
In one line, that would give:
lines = open('C:/path/file.txt').read().splitlines()
However, this is quite inefficient way as this will store 2 versions of the content in memory (probably not a big issue for small files, but still). [Thanks Mark Amery].
There are 2 easier ways:
Using the file as an iterator
lines = list(open('C:/path/file.txt'))
# ... or if you want to have a list without EOL characters
lines = [l.rstrip() for l in open('C:/path/file.txt')]
If you are using Python 3.4 or above, better use pathlib to create a path for your file that you could use for other operations in your program:
from pathlib import Path
file_path = Path("C:/path/file.txt")
lines = file_path.read_text().split_lines()
# ... or ...
lines = [l.rstrip() for l in file_path.open()]

Just use the splitlines() functions. Here is an example.
inp = "file.txt"
data = open(inp)
dat = data.read()
lst = dat.splitlines()
print lst
# print(lst) # for python 3
In the output you will have the list of lines.

If you are faced with a very large / huge file and want to read faster (imagine you are in a TopCoder or HackerRank coding competition), you might read a considerably bigger chunk of lines into a memory buffer at one time, rather than just iterate line by line at file level.
buffersize = 2**16
with open(path) as f:
while True:
lines_buffer = f.readlines(buffersize)
if not lines_buffer:
break
for line in lines_buffer:
process(line)

The easiest ways to do that with some additional benefits are:
lines = list(open('filename'))
or
lines = tuple(open('filename'))
or
lines = set(open('filename'))
In the case with set, we must be remembered that we don't have the line order preserved and get rid of the duplicated lines.
Below I added an important supplement from #MarkAmery:
Since you're not calling .close on the file object nor using a with statement, in some Python implementations the file may not get closed after reading and your process will leak an open file handle.
In CPython (the normal Python implementation that most people use), this isn't a problem since the file object will get immediately garbage-collected and this will close the file, but it's nonetheless generally considered best practice to do something like:
with open('filename') as f: lines = list(f)
to ensure that the file gets closed regardless of what Python implementation you're using.

Use this:
import pandas as pd
data = pd.read_csv(filename) # You can also add parameters such as header, sep, etc.
array = data.values
data is a dataframe type, and uses values to get ndarray. You can also get a list by using array.tolist().

In case that there are also empty lines in the document I like to read in the content and pass it through filter to prevent empty string elements
with open(myFile, "r") as f:
excludeFileContent = list(filter(None, f.read().splitlines()))

Outline and Summary
With a filename, handling the file from a Path(filename) object, or directly with open(filename) as f, do one of the following:
list(fileinput.input(filename))
using with path.open() as f, call f.readlines()
list(f)
path.read_text().splitlines()
path.read_text().splitlines(keepends=True)
iterate over fileinput.input or f and list.append each line one at a time
pass f to a bound list.extend method
use f in a list comprehension
I explain the use-case for each below.
In Python, how do I read a file line-by-line?
This is an excellent question. First, let's create some sample data:
from pathlib import Path
Path('filename').write_text('foo\nbar\nbaz')
File objects are lazy iterators, so just iterate over it.
filename = 'filename'
with open(filename) as f:
for line in f:
line # do something with the line
Alternatively, if you have multiple files, use fileinput.input, another lazy iterator. With just one file:
import fileinput
for line in fileinput.input(filename):
line # process the line
or for multiple files, pass it a list of filenames:
for line in fileinput.input([filename]*2):
line # process the line
Again, f and fileinput.input above both are/return lazy iterators.
You can only use an iterator one time, so to provide functional code while avoiding verbosity I'll use the slightly more terse fileinput.input(filename) where apropos from here.
In Python, how do I read a file line-by-line into a list?
Ah but you want it in a list for some reason? I'd avoid that if possible. But if you insist... just pass the result of fileinput.input(filename) to list:
list(fileinput.input(filename))
Another direct answer is to call f.readlines, which returns the contents of the file (up to an optional hint number of characters, so you could break this up into multiple lists that way).
You can get to this file object two ways. One way is to pass the filename to the open builtin:
filename = 'filename'
with open(filename) as f:
f.readlines()
or using the new Path object from the pathlib module (which I have become quite fond of, and will use from here on):
from pathlib import Path
path = Path(filename)
with path.open() as f:
f.readlines()
list will also consume the file iterator and return a list - a quite direct method as well:
with path.open() as f:
list(f)
If you don't mind reading the entire text into memory as a single string before splitting it, you can do this as a one-liner with the Path object and the splitlines() string method. By default, splitlines removes the newlines:
path.read_text().splitlines()
If you want to keep the newlines, pass keepends=True:
path.read_text().splitlines(keepends=True)
I want to read the file line by line and append each line to the end of the list.
Now this is a bit silly to ask for, given that we've demonstrated the end result easily with several methods. But you might need to filter or operate on the lines as you make your list, so let's humor this request.
Using list.append would allow you to filter or operate on each line before you append it:
line_list = []
for line in fileinput.input(filename):
line_list.append(line)
line_list
Using list.extend would be a bit more direct, and perhaps useful if you have a preexisting list:
line_list = []
line_list.extend(fileinput.input(filename))
line_list
Or more idiomatically, we could instead use a list comprehension, and map and filter inside it if desirable:
[line for line in fileinput.input(filename)]
Or even more directly, to close the circle, just pass it to list to create a new list directly without operating on the lines:
list(fileinput.input(filename))
Conclusion
You've seen many ways to get lines from a file into a list, but I'd recommend you avoid materializing large quantities of data into a list and instead use Python's lazy iteration to process the data if possible.
That is, prefer fileinput.input or with path.open() as f.

I would try one of the below mentioned methods. The example file that I use has the name dummy.txt. You can find the file here. I presume that the file is in the same directory as the code (you can change fpath to include the proper file name and folder path).
In both the below mentioned examples, the list that you want is given by lst.
1. First method
fpath = 'dummy.txt'
with open(fpath, "r") as f: lst = [line.rstrip('\n \t') for line in f]
print lst
>>>['THIS IS LINE1.', 'THIS IS LINE2.', 'THIS IS LINE3.', 'THIS IS LINE4.']
2. In the second method, one can use csv.reader module from Python Standard Library:
import csv
fpath = 'dummy.txt'
with open(fpath) as csv_file:
csv_reader = csv.reader(csv_file, delimiter=' ')
lst = [row[0] for row in csv_reader]
print lst
>>>['THIS IS LINE1.', 'THIS IS LINE2.', 'THIS IS LINE3.', 'THIS IS LINE4.']
You can use either of the two methods. The time taken for the creation of lst is almost equal for the two methods.

I like to use the following. Reading the lines immediately.
contents = []
for line in open(filepath, 'r').readlines():
contents.append(line.strip())
Or using list comprehension:
contents = [line.strip() for line in open(filepath, 'r').readlines()]

You could also use the loadtxt command in NumPy. This checks for fewer conditions than genfromtxt, so it may be faster.
import numpy
data = numpy.loadtxt(filename, delimiter="\n")

Here is a Python(3) helper library class that I use to simplify file I/O:
import os
# handle files using a callback method, prevents repetition
def _FileIO__file_handler(file_path, mode, callback = lambda f: None):
f = open(file_path, mode)
try:
return callback(f)
except Exception as e:
raise IOError("Failed to %s file" % ["write to", "read from"][mode.lower() in "r rb r+".split(" ")])
finally:
f.close()
class FileIO:
# return the contents of a file
def read(file_path, mode = "r"):
return __file_handler(file_path, mode, lambda rf: rf.read())
# get the lines of a file
def lines(file_path, mode = "r", filter_fn = lambda line: len(line) > 0):
return [line for line in FileIO.read(file_path, mode).strip().split("\n") if filter_fn(line)]
# create or update a file (NOTE: can also be used to replace a file's original content)
def write(file_path, new_content, mode = "w"):
return __file_handler(file_path, mode, lambda wf: wf.write(new_content))
# delete a file (if it exists)
def delete(file_path):
return os.remove() if os.path.isfile(file_path) else None
You would then use the FileIO.lines function, like this:
file_ext_lines = FileIO.lines("./path/to/file.ext"):
for i, line in enumerate(file_ext_lines):
print("Line {}: {}".format(i + 1, line))
Remember that the mode ("r" by default) and filter_fn (checks for empty lines by default) parameters are optional.
You could even remove the read, write and delete methods and just leave the FileIO.lines, or even turn it into a separate method called read_lines.

Command line version
#!/bin/python3
import os
import sys
abspath = os.path.abspath(__file__)
dname = os.path.dirname(abspath)
filename = dname + sys.argv[1]
arr = open(filename).read().split("\n")
print(arr)
Run with:
python3 somefile.py input_file_name.txt

how to read data from file in pandas [duplicate]

This question's answers are a community effort. Edit existing answers to improve this post. It is not currently accepting new answers or interactions.
How do I read every line of a file in Python and store each line as an element in a list?
I want to read the file line by line and append each line to the end of the list.

This code will read the entire file into memory and remove all whitespace characters (newlines and spaces) from the end of each line:
with open(filename) as file:
lines = [line.rstrip() for line in file]
If you're working with a large file, then you should instead read and process it line-by-line:
with open(filename) as file:
for line in file:
print(line.rstrip())
In Python 3.8 and up you can use a while loop with the walrus operator like so:
with open(filename) as file:
while (line := file.readline().rstrip()):
print(line)
Depending on what you plan to do with your file and how it was encoded, you may also want to manually set the access mode and character encoding:
with open(filename, 'r', encoding='UTF-8') as file:
while (line := file.readline().rstrip()):
print(line)

See Input and Ouput:
with open('filename') as f:
lines = f.readlines()
or with stripping the newline character:
with open('filename') as f:
lines = [line.rstrip('\n') for line in f]

This is more explicit than necessary, but does what you want.
with open("file.txt") as file_in:
lines = []
for line in file_in:
lines.append(line)

This will yield an "array" of lines from the file.
lines = tuple(open(filename, 'r'))
open returns a file which can be iterated over. When you iterate over a file, you get the lines from that file. tuple can take an iterator and instantiate a tuple instance for you from the iterator that you give it. lines is a tuple created from the lines of the file.

According to Python's Methods of File Objects, the simplest way to convert a text file into a list is:
with open('file.txt') as f:
my_list = list(f)
# my_list = [x.rstrip() for x in f] # remove line breaks
Demo
If you just need to iterate over the text file lines, you can use:
with open('file.txt') as f:
for line in f:
...
Old answer:
Using with and readlines() :
with open('file.txt') as f:
lines = f.readlines()
If you don't care about closing the file, this one-liner will work:
lines = open('file.txt').readlines()
The traditional way:
f = open('file.txt') # Open file on read mode
lines = f.read().splitlines() # List with stripped line-breaks
f.close() # Close file

If you want the \n included:
with open(fname) as f:
content = f.readlines()
If you do not want \n included:
with open(fname) as f:
content = f.read().splitlines()

You could simply do the following, as has been suggested:
with open('/your/path/file') as f:
my_lines = f.readlines()
Note that this approach has 2 downsides:
1) You store all the lines in memory. In the general case, this is a very bad idea. The file could be very large, and you could run out of memory. Even if it's not large, it is simply a waste of memory.
2) This does not allow processing of each line as you read them. So if you process your lines after this, it is not efficient (requires two passes rather than one).
A better approach for the general case would be the following:
with open('/your/path/file') as f:
for line in f:
process(line)
Where you define your process function any way you want. For example:
def process(line):
if 'save the world' in line.lower():
superman.save_the_world()
(The implementation of the Superman class is left as an exercise for you).
This will work nicely for any file size and you go through your file in just 1 pass. This is typically how generic parsers will work.

Having a Text file content:
line 1
line 2
line 3
We can use this Python script in the same directory of the txt above
>>> with open("myfile.txt", encoding="utf-8") as file:
... x = [l.rstrip("\n") for l in file]
>>> x
['line 1','line 2','line 3']
Using append:
x = []
with open("myfile.txt") as file:
for l in file:
x.append(l.strip())
Or:
>>> x = open("myfile.txt").read().splitlines()
>>> x
['line 1', 'line 2', 'line 3']
Or:
>>> x = open("myfile.txt").readlines()
>>> x
['linea 1\n', 'line 2\n', 'line 3\n']
Or:
def print_output(lines_in_textfile):
print("lines_in_textfile =", lines_in_textfile)
y = [x.rstrip() for x in open("001.txt")]
print_output(y)
with open('001.txt', 'r', encoding='utf-8') as file:
file = file.read().splitlines()
print_output(file)
with open('001.txt', 'r', encoding='utf-8') as file:
file = [x.rstrip("\n") for x in file]
print_output(file)
output:
lines_in_textfile = ['line 1', 'line 2', 'line 3']
lines_in_textfile = ['line 1', 'line 2', 'line 3']
lines_in_textfile = ['line 1', 'line 2', 'line 3']

Introduced in Python 3.4, pathlib has a really convenient method for reading in text from files, as follows:
from pathlib import Path
p = Path('my_text_file')
lines = p.read_text().splitlines()
(The splitlines call is what turns it from a string containing the whole contents of the file to a list of lines in the file.)
pathlib has a lot of handy conveniences in it. read_text is nice and concise, and you don't have to worry about opening and closing the file. If all you need to do with the file is read it all in in one go, it's a good choice.

To read a file into a list you need to do three things:
Open the file
Read the file
Store the contents as list
Fortunately Python makes it very easy to do these things so the shortest way to read a file into a list is:
lst = list(open(filename))
However I'll add some more explanation.
Opening the file
I assume that you want to open a specific file and you don't deal directly with a file-handle (or a file-like-handle). The most commonly used function to open a file in Python is open, it takes one mandatory argument and two optional ones in Python 2.7:
Filename
Mode
Buffering (I'll ignore this argument in this answer)
The filename should be a string that represents the path to the file. For example:
open('afile') # opens the file named afile in the current working directory
open('adir/afile') # relative path (relative to the current working directory)
open('C:/users/aname/afile') # absolute path (windows)
open('/usr/local/afile') # absolute path (linux)
Note that the file extension needs to be specified. This is especially important for Windows users because file extensions like .txt or .doc, etc. are hidden by default when viewed in the explorer.
The second argument is the mode, it's r by default which means "read-only". That's exactly what you need in your case.
But in case you actually want to create a file and/or write to a file you'll need a different argument here. There is an excellent answer if you want an overview.
For reading a file you can omit the mode or pass it in explicitly:
open(filename)
open(filename, 'r')
Both will open the file in read-only mode. In case you want to read in a binary file on Windows you need to use the mode rb:
open(filename, 'rb')
On other platforms the 'b' (binary mode) is simply ignored.
Now that I've shown how to open the file, let's talk about the fact that you always need to close it again. Otherwise it will keep an open file-handle to the file until the process exits (or Python garbages the file-handle).
While you could use:
f = open(filename)
# ... do stuff with f
f.close()
That will fail to close the file when something between open and close throws an exception. You could avoid that by using a try and finally:
f = open(filename)
# nothing in between!
try:
# do stuff with f
finally:
f.close()
However Python provides context managers that have a prettier syntax (but for open it's almost identical to the try and finally above):
with open(filename) as f:
# do stuff with f
# The file is always closed after the with-scope ends.
The last approach is the recommended approach to open a file in Python!
Reading the file
Okay, you've opened the file, now how to read it?
The open function returns a file object and it supports Pythons iteration protocol. Each iteration will give you a line:
with open(filename) as f:
for line in f:
print(line)
This will print each line of the file. Note however that each line will contain a newline character \n at the end (you might want to check if your Python is built with universal newlines support - otherwise you could also have \r\n on Windows or \r on Mac as newlines). If you don't want that you can could simply remove the last character (or the last two characters on Windows):
with open(filename) as f:
for line in f:
print(line[:-1])
But the last line doesn't necessarily has a trailing newline, so one shouldn't use that. One could check if it ends with a trailing newline and if so remove it:
with open(filename) as f:
for line in f:
if line.endswith('\n'):
line = line[:-1]
print(line)
But you could simply remove all whitespaces (including the \n character) from the end of the string, this will also remove all other trailing whitespaces so you have to be careful if these are important:
with open(filename) as f:
for line in f:
print(f.rstrip())
However if the lines end with \r\n (Windows "newlines") that .rstrip() will also take care of the \r!
Store the contents as list
Now that you know how to open the file and read it, it's time to store the contents in a list. The simplest option would be to use the list function:
with open(filename) as f:
lst = list(f)
In case you want to strip the trailing newlines you could use a list comprehension instead:
with open(filename) as f:
lst = [line.rstrip() for line in f]
Or even simpler: The .readlines() method of the file object by default returns a list of the lines:
with open(filename) as f:
lst = f.readlines()
This will also include the trailing newline characters, if you don't want them I would recommend the [line.rstrip() for line in f] approach because it avoids keeping two lists containing all the lines in memory.
There's an additional option to get the desired output, however it's rather "suboptimal": read the complete file in a string and then split on newlines:
with open(filename) as f:
lst = f.read().split('\n')
or:
with open(filename) as f:
lst = f.read().splitlines()
These take care of the trailing newlines automatically because the split character isn't included. However they are not ideal because you keep the file as string and as a list of lines in memory!
Summary
Use with open(...) as f when opening files because you don't need to take care of closing the file yourself and it closes the file even if some exception happens.
file objects support the iteration protocol so reading a file line-by-line is as simple as for line in the_file_object:.
Always browse the documentation for the available functions/classes. Most of the time there's a perfect match for the task or at least one or two good ones. The obvious choice in this case would be readlines() but if you want to process the lines before storing them in the list I would recommend a simple list-comprehension.

Clean and Pythonic Way of Reading the Lines of a File Into a List
First and foremost, you should focus on opening your file and reading its contents in an efficient and pythonic way. Here is an example of the way I personally DO NOT prefer:
infile = open('my_file.txt', 'r') # Open the file for reading.
data = infile.read() # Read the contents of the file.
infile.close() # Close the file since we're done using it.
Instead, I prefer the below method of opening files for both reading and writing as it
is very clean, and does not require an extra step of closing the file
once you are done using it. In the statement below, we're opening the file
for reading, and assigning it to the variable 'infile.' Once the code within
this statement has finished running, the file will be automatically closed.
# Open the file for reading.
with open('my_file.txt', 'r') as infile:
data = infile.read() # Read the contents of the file into memory.
Now we need to focus on bringing this data into a Python List because they are iterable, efficient, and flexible. In your case, the desired goal is to bring each line of the text file into a separate element. To accomplish this, we will use the splitlines() method as follows:
# Return a list of the lines, breaking at line boundaries.
my_list = data.splitlines()
The Final Product:
# Open the file for reading.
with open('my_file.txt', 'r') as infile:
data = infile.read() # Read the contents of the file into memory.
# Return a list of the lines, breaking at line boundaries.
my_list = data.splitlines()
Testing Our Code:
Contents of the text file:
A fost odatã ca-n povesti,
A fost ca niciodatã,
Din rude mãri împãrãtesti,
O prea frumoasã fatã.
Print statements for testing purposes:
print my_list # Print the list.
# Print each line in the list.
for line in my_list:
print line
# Print the fourth element in this list.
print my_list[3]
Output (different-looking because of unicode characters):
['A fost odat\xc3\xa3 ca-n povesti,', 'A fost ca niciodat\xc3\xa3,',
'Din rude m\xc3\xa3ri \xc3\xaemp\xc3\xa3r\xc3\xa3testi,', 'O prea
frumoas\xc3\xa3 fat\xc3\xa3.']
A fost odatã ca-n povesti, A fost ca niciodatã, Din rude mãri
împãrãtesti, O prea frumoasã fatã.
O prea frumoasã fatã.

Here's one more option by using list comprehensions on files;
lines = [line.rstrip() for line in open('file.txt')]
This should be more efficient way as the most of the work is done inside the Python interpreter.

f = open("your_file.txt",'r')
out = f.readlines() # will append in the list out
Now variable out is a list (array) of what you want. You could either do:
for line in out:
print (line)
Or:
for line in f:
print (line)
You'll get the same results.

Another option is numpy.genfromtxt, for example:
import numpy as np
data = np.genfromtxt("yourfile.dat",delimiter="\n")
This will make data a NumPy array with as many rows as are in your file.

Read and write text files with Python 2 and Python 3; it works with Unicode
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# Define data
lines = [' A first string ',
'A Unicode sample: €',
'German: äöüß']
# Write text file
with open('file.txt', 'w') as fp:
fp.write('\n'.join(lines))
# Read text file
with open('file.txt', 'r') as fp:
read_lines = fp.readlines()
read_lines = [line.rstrip('\n') for line in read_lines]
print(lines == read_lines)
Things to notice:
with is a so-called context manager. It makes sure that the opened file is closed again.
All solutions here which simply make .strip() or .rstrip() will fail to reproduce the lines as they also strip the white space.
Common file endings
.txt
More advanced file writing/reading
CSV: Super simple format (read & write)
JSON: Nice for writing human-readable data; VERY commonly used (read & write)
YAML: YAML is a superset of JSON, but easier to read (read & write, comparison of JSON and YAML)
pickle: A Python serialization format (read & write)
MessagePack (Python package): More compact representation (read & write)
HDF5 (Python package): Nice for matrices (read & write)
XML: exists too *sigh* (read & write)
For your application, the following might be important:
Support by other programming languages
Reading/writing performance
Compactness (file size)
See also: Comparison of data serialization formats
In case you are rather looking for a way to make configuration files, you might want to read my short article Configuration files in Python.

If you'd like to read a file from the command line or from stdin, you can also use the fileinput module:
# reader.py
import fileinput
content = []
for line in fileinput.input():
content.append(line.strip())
fileinput.close()
Pass files to it like so:
$ python reader.py textfile.txt
Read more here: http://docs.python.org/2/library/fileinput.html

The simplest way to do it
A simple way is to:
Read the whole file as a string
Split the string line by line
In one line, that would give:
lines = open('C:/path/file.txt').read().splitlines()
However, this is quite inefficient way as this will store 2 versions of the content in memory (probably not a big issue for small files, but still). [Thanks Mark Amery].
There are 2 easier ways:
Using the file as an iterator
lines = list(open('C:/path/file.txt'))
# ... or if you want to have a list without EOL characters
lines = [l.rstrip() for l in open('C:/path/file.txt')]
If you are using Python 3.4 or above, better use pathlib to create a path for your file that you could use for other operations in your program:
from pathlib import Path
file_path = Path("C:/path/file.txt")
lines = file_path.read_text().split_lines()
# ... or ...
lines = [l.rstrip() for l in file_path.open()]

Just use the splitlines() functions. Here is an example.
inp = "file.txt"
data = open(inp)
dat = data.read()
lst = dat.splitlines()
print lst
# print(lst) # for python 3
In the output you will have the list of lines.

If you are faced with a very large / huge file and want to read faster (imagine you are in a TopCoder or HackerRank coding competition), you might read a considerably bigger chunk of lines into a memory buffer at one time, rather than just iterate line by line at file level.
buffersize = 2**16
with open(path) as f:
while True:
lines_buffer = f.readlines(buffersize)
if not lines_buffer:
break
for line in lines_buffer:
process(line)

The easiest ways to do that with some additional benefits are:
lines = list(open('filename'))
or
lines = tuple(open('filename'))
or
lines = set(open('filename'))
In the case with set, we must be remembered that we don't have the line order preserved and get rid of the duplicated lines.
Below I added an important supplement from #MarkAmery:
Since you're not calling .close on the file object nor using a with statement, in some Python implementations the file may not get closed after reading and your process will leak an open file handle.
In CPython (the normal Python implementation that most people use), this isn't a problem since the file object will get immediately garbage-collected and this will close the file, but it's nonetheless generally considered best practice to do something like:
with open('filename') as f: lines = list(f)
to ensure that the file gets closed regardless of what Python implementation you're using.

Use this:
import pandas as pd
data = pd.read_csv(filename) # You can also add parameters such as header, sep, etc.
array = data.values
data is a dataframe type, and uses values to get ndarray. You can also get a list by using array.tolist().

In case that there are also empty lines in the document I like to read in the content and pass it through filter to prevent empty string elements
with open(myFile, "r") as f:
excludeFileContent = list(filter(None, f.read().splitlines()))

Outline and Summary
With a filename, handling the file from a Path(filename) object, or directly with open(filename) as f, do one of the following:
list(fileinput.input(filename))
using with path.open() as f, call f.readlines()
list(f)
path.read_text().splitlines()
path.read_text().splitlines(keepends=True)
iterate over fileinput.input or f and list.append each line one at a time
pass f to a bound list.extend method
use f in a list comprehension
I explain the use-case for each below.
In Python, how do I read a file line-by-line?
This is an excellent question. First, let's create some sample data:
from pathlib import Path
Path('filename').write_text('foo\nbar\nbaz')
File objects are lazy iterators, so just iterate over it.
filename = 'filename'
with open(filename) as f:
for line in f:
line # do something with the line
Alternatively, if you have multiple files, use fileinput.input, another lazy iterator. With just one file:
import fileinput
for line in fileinput.input(filename):
line # process the line
or for multiple files, pass it a list of filenames:
for line in fileinput.input([filename]*2):
line # process the line
Again, f and fileinput.input above both are/return lazy iterators.
You can only use an iterator one time, so to provide functional code while avoiding verbosity I'll use the slightly more terse fileinput.input(filename) where apropos from here.
In Python, how do I read a file line-by-line into a list?
Ah but you want it in a list for some reason? I'd avoid that if possible. But if you insist... just pass the result of fileinput.input(filename) to list:
list(fileinput.input(filename))
Another direct answer is to call f.readlines, which returns the contents of the file (up to an optional hint number of characters, so you could break this up into multiple lists that way).
You can get to this file object two ways. One way is to pass the filename to the open builtin:
filename = 'filename'
with open(filename) as f:
f.readlines()
or using the new Path object from the pathlib module (which I have become quite fond of, and will use from here on):
from pathlib import Path
path = Path(filename)
with path.open() as f:
f.readlines()
list will also consume the file iterator and return a list - a quite direct method as well:
with path.open() as f:
list(f)
If you don't mind reading the entire text into memory as a single string before splitting it, you can do this as a one-liner with the Path object and the splitlines() string method. By default, splitlines removes the newlines:
path.read_text().splitlines()
If you want to keep the newlines, pass keepends=True:
path.read_text().splitlines(keepends=True)
I want to read the file line by line and append each line to the end of the list.
Now this is a bit silly to ask for, given that we've demonstrated the end result easily with several methods. But you might need to filter or operate on the lines as you make your list, so let's humor this request.
Using list.append would allow you to filter or operate on each line before you append it:
line_list = []
for line in fileinput.input(filename):
line_list.append(line)
line_list
Using list.extend would be a bit more direct, and perhaps useful if you have a preexisting list:
line_list = []
line_list.extend(fileinput.input(filename))
line_list
Or more idiomatically, we could instead use a list comprehension, and map and filter inside it if desirable:
[line for line in fileinput.input(filename)]
Or even more directly, to close the circle, just pass it to list to create a new list directly without operating on the lines:
list(fileinput.input(filename))
Conclusion
You've seen many ways to get lines from a file into a list, but I'd recommend you avoid materializing large quantities of data into a list and instead use Python's lazy iteration to process the data if possible.
That is, prefer fileinput.input or with path.open() as f.

I would try one of the below mentioned methods. The example file that I use has the name dummy.txt. You can find the file here. I presume that the file is in the same directory as the code (you can change fpath to include the proper file name and folder path).
In both the below mentioned examples, the list that you want is given by lst.
1. First method
fpath = 'dummy.txt'
with open(fpath, "r") as f: lst = [line.rstrip('\n \t') for line in f]
print lst
>>>['THIS IS LINE1.', 'THIS IS LINE2.', 'THIS IS LINE3.', 'THIS IS LINE4.']
2. In the second method, one can use csv.reader module from Python Standard Library:
import csv
fpath = 'dummy.txt'
with open(fpath) as csv_file:
csv_reader = csv.reader(csv_file, delimiter=' ')
lst = [row[0] for row in csv_reader]
print lst
>>>['THIS IS LINE1.', 'THIS IS LINE2.', 'THIS IS LINE3.', 'THIS IS LINE4.']
You can use either of the two methods. The time taken for the creation of lst is almost equal for the two methods.

I like to use the following. Reading the lines immediately.
contents = []
for line in open(filepath, 'r').readlines():
contents.append(line.strip())
Or using list comprehension:
contents = [line.strip() for line in open(filepath, 'r').readlines()]

You could also use the loadtxt command in NumPy. This checks for fewer conditions than genfromtxt, so it may be faster.
import numpy
data = numpy.loadtxt(filename, delimiter="\n")

Here is a Python(3) helper library class that I use to simplify file I/O:
import os
# handle files using a callback method, prevents repetition
def _FileIO__file_handler(file_path, mode, callback = lambda f: None):
f = open(file_path, mode)
try:
return callback(f)
except Exception as e:
raise IOError("Failed to %s file" % ["write to", "read from"][mode.lower() in "r rb r+".split(" ")])
finally:
f.close()
class FileIO:
# return the contents of a file
def read(file_path, mode = "r"):
return __file_handler(file_path, mode, lambda rf: rf.read())
# get the lines of a file
def lines(file_path, mode = "r", filter_fn = lambda line: len(line) > 0):
return [line for line in FileIO.read(file_path, mode).strip().split("\n") if filter_fn(line)]
# create or update a file (NOTE: can also be used to replace a file's original content)
def write(file_path, new_content, mode = "w"):
return __file_handler(file_path, mode, lambda wf: wf.write(new_content))
# delete a file (if it exists)
def delete(file_path):
return os.remove() if os.path.isfile(file_path) else None
You would then use the FileIO.lines function, like this:
file_ext_lines = FileIO.lines("./path/to/file.ext"):
for i, line in enumerate(file_ext_lines):
print("Line {}: {}".format(i + 1, line))
Remember that the mode ("r" by default) and filter_fn (checks for empty lines by default) parameters are optional.
You could even remove the read, write and delete methods and just leave the FileIO.lines, or even turn it into a separate method called read_lines.

Command line version
#!/bin/python3
import os
import sys
abspath = os.path.abspath(__file__)
dname = os.path.dirname(abspath)
filename = dname + sys.argv[1]
arr = open(filename).read().split("\n")
print(arr)
Run with:
python3 somefile.py input_file_name.txt

How to efficiently append a new line to the starting of a large file?

I want to append a new line in the starting of 2GB+ file. I tried following code but code OUT of MEMORY
error.
myfile = open(tableTempFile, "r+")
myfile.read() # read everything in the file
myfile.seek(0) # rewind
myfile.write("WRITE IN THE FIRST LINE ")
myfile.close();
What is the way to write in a file file without getting the entire file in memory?
How to append a new line at starting of the file?

Please note, there's no way to do this with any built-in functions in Python.
You can do this easily in LINUX using tail / cat etc.
For doing it via Python we must use an auxiliary file and for doing this with very large files, I think this method is the possibility:
def add_line_at_start(filename,line_to_be_added):
f = fileinput.input(filename,inplace=1)
for xline in f:
if f.isfirstline():
print line_to_be_added.rstrip('\r\n') + '\n' + xline,
else:
print xline
NOTE:
Never try to use read() / readlines() functions when you are dealing with big files. These methods tried load the complete file into your memory
In your given code, seek function is going to take you the starting point but then everything you write would overwrite the current content

If you can afford having the entire file in memory at once:
first_line_update = "WRITE IN THE FIRST LINE \n"
with open(tableTempFile, 'r+') as f:
lines = f.readlines()
lines[0] = first_line_update
f.writelines(lines)
otherwise:
from shutil import copy
from itertools import islice, chain
# TODO: use a NamedTemporaryFile from the tempfile module
first_line_update = "WRITE IN THE FIRST LINE \n"
with open("inputfile", 'r') as infile, open("tmpfile", 'w+') as outfile:
# replace the first line with the string provided:
outfile.writelines(
(line for line in chain((first_line_update,), islice(infile,1,None)))
# if you don't want to replace the first line but to insert another line before
# this simplifies to:
#outfile.writelines(line for line in chain((first_line_update,), infile))
copy("tmpfile", "infile")
# TODO: remove temporary file

Generally, you can't do that. A file is a sequence of bytes, not a sequence of lines. This data model doesn't allow for insertions in arbitrary points - you can either replace a byte by another or append bytes at the end.
You can either:
Replace the first X bytes in the file. This could work for you if you can make sure that the first line's length will never vary.
Truncate the file, write the first line, then rewrite all the rest after it. If you can't fit all your file into the memory, then:
create a temporary file (the tempfile module will help you)
write your line to it
open your base file in r and copy its contents after the first line to the temporary file, piece-wise
close both files, then replace the input file by the temporary file
(Note that appending to the end of a file is much easier - all you need to do is open the file in the append a mode.)

How do I modify the last line of a file?

The last line of my file is:
29-dez,40,
How can I modify that line so that it reads:
29-Dez,40,90,100,50
Note: I don't want to write a new line. I want to take the same line and put new values after 29-Dez,40,
I'm new at python. I'm having a lot of trouble manipulating files and for me every example I look at seems difficult.

Unless the file is huge, you'll probably find it easier to read the entire file into a data structure (which might just be a list of lines), and then modify the data structure in memory, and finally write it back to the file.
On the other hand maybe your file is really huge - multiple GBs at least. In which case: the last line is probably terminated with a new line character, if you seek to that position you can overwrite it with the new text at the end of the last line.
So perhaps:
f = open("foo.file", "wb")
f.seek(-len(os.linesep), os.SEEK_END)
f.write("new text at end of last line" + os.linesep)
f.close()
(Modulo line endings on different platforms)

To expand on what Doug said, in order to read the file contents into a data structure you can use the readlines() method of the file object.
The below code sample reads the file into a list of "lines", edits the last line, then writes it back out to the file:
#!/usr/bin/python
MYFILE="file.txt"
# read the file into a list of lines
lines = open(MYFILE, 'r').readlines()
# now edit the last line of the list of lines
new_last_line = (lines[-1].rstrip() + ",90,100,50")
lines[-1] = new_last_line
# now write the modified list back out to the file
open(MYFILE, 'w').writelines(lines)
If the file is very large then this approach will not work well, because this reads all the file lines into memory each time and writes them back out to the file, which is very inefficient. For a small file however this will work fine.

Don't work with files directly, make a data structure that fits your needs in form of a class and make read from/write to file methods.

I recently wrote a script to do something very similar to this. It would traverse a project, find all module dependencies and add any missing import statements. I won't clutter this post up with the entire script, but I'll show how I went about modifying my files.
import os
from mmap import mmap
def insert_import(filename, text):
if len(text) < 1:
return
f = open(filename, 'r+')
m = mmap(f.fileno(), os.path.getsize(filename))
origSize = m.size()
m.resize(origSize + len(text))
pos = 0
while True:
l = m.readline()
if l.startswith(('import', 'from')):
continue
else:
pos = m.tell() - len(l)
break
m[pos+len(text):] = m[pos:origSize]
m[pos:pos+len(text)] = text
m.close()
f.close()
Summary: This snippet takes a filename and a blob of text to insert. It finds the last import statement already present, and sticks the text in at that location.
The part I suggest paying most attention to is the use of mmap. It lets you work with files in the same manner you may work with a string. Very handy.