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How to open a file in python, read the comments ("#"), find a word after the comments and select the word after it?

I have a function that loops through a file that Looks like this:
"#" XDI/1.0 XDAC/1.4 Athena/0.9.25
"#" Column.4: pre_edge
Content
That is to say that after the "#" there is a comment. My function aims to read each line and if it starts with a specific word, select what is after the ":"
For example if I had These two lines. I would like to read through them and if the line starts with "#" and contains the word "Column.4" the word "pre_edge" should be stored.
An example of my current approach follows:
with open(file, "r") as f:
for line in f:
if line.startswith ('#'):
word = line.split(" Column.4:")[1]
else:
print("n")
I think my Trouble is specifically after finding a line that starts with "#" how can I parse/search through it? and save its Content if it contains the desidered word.

In case that # comment contain str Column.4: as stated above, you could parse it this way.
with open(filepath) as f:
for line in f:
if line.startswith('#'):
# Here you proceed comment lines
if 'Column.4' in line:
first, remainder = line.split('Column.4: ')
# Remainder contains everything after '# Column.4: '
# So if you want to get first word ->
word = remainder.split()[0]
else:
# Here you can proceed lines that are not comments
pass
Note
Also it is a good practice to use for line in f: statement instead of f.readlines() (as mentioned in other answers), because this way you don't load all lines into memory, but proceed them one by one.

You should start by reading the file into a list and then work through that instead:
file = 'test.txt' #<- call file whatever you want
with open(file, "r") as f:
txt = f.readlines()
for line in txt:
if line.startswith ('"#"'):
word = line.split(" Column.4: ")
try:
print(word[1])
except IndexError:
print(word)
else:
print("n")
Output:
>>> ['"#" XDI/1.0 XDAC/1.4 Athena/0.9.25\n']
>>> pre_edge
Used a try and except catch because the first line also starts with "#" and we can't split that with your current logic.
Also, as a side note, in the question you have the file with lines starting as "#" with the quotation marks so the startswith() function was altered as such.

with open('stuff.txt', 'r+') as f:
data = f.readlines()
for line in data:
words = line.split()
if words and ('#' in words[0]) and ("Column.4:" in words):
print(words[-1])
# pre_edge

delete empty spaces of files python

I have a file with several lines, and some of them have empty spaces.
x=20
y=3
z = 1.5
v = 0.1
I want to delete those spaces and get each line into a dictionary, where the element before the '=' sign will be the key, and the element after the '=' sign will be its value.
However, my code is not working, at least the "delete empty spaces" part. Here's the code:
def copyFile(filename):
"""
function's contract
"""
with open(filename, 'r') as inFile:
for line in inFile:
cleanedLine = line.strip()
if cleanedLine:
firstPart, secondPart = line.split('=')
dic[firstPart] = float(secondPart)
inFile.close()
return dic
After clearing the empty spaces, my file is supposed to get like this
x=20
y=3
z=1.5
v=0.1
But is not working. What am I doing wrong?

You need to strip after splitting the string. That's assuming that the only unwanted spaces are around the = or before or after the contents of the line.
from ast import literal_eval
def copyFile(filename):
with open(filename, 'r') as inFile:
split_lines = (line.split('=', 1) for line in inFile)
d = {key.strip(): literal_eval(value.strip()) for key, value in split_lines}
return d

There are a few issues with your code.
For one, you never define dic so when you try to add keys to it you get a NameError.
Second, you don't need to inFile.close() because you're opening it in a with which will always close it outside the block.
Third, your function and variable names are not PEP8 standard.
Fourth, you need to strip each part.
Here's some code that works and looks nice:
def copy_file(filename):
"""
function's contract
"""
dic = {}
with open(filename, 'r') as in_file:
for line in in_file:
cleaned_line = line.strip()
if cleaned_line:
first_part, second_part = line.split('=')
dic[first_part.strip()] = float(second_part.strip())
return dic

You have two problems:
The reason you're not removing the white space is that you're calling .strip() on the entire line. strip() removes white space at the beginning and end of the string, not in the middle. Instead, called .strip() on firstpart and lastpart.
That will fix the in-memory dictionary that you're creating but it won't make any changes to the file since you're never writing to the file. You'll want to create a second copy of the file into which you write your strip()ed values and then, at the end, replace the original file with the new file.

to remove the whitespace try .replace(" ", "") instead of .strip()

how can i convert surname:name to name:surname? [duplicate]

In Python, calling e.g. temp = open(filename,'r').readlines() results in a list in which each element is a line from the file. However, these strings have a newline character at the end, which I don't want.
How can I get the data without the newlines?

You can read the whole file and split lines using str.splitlines:
temp = file.read().splitlines()
Or you can strip the newline by hand:
temp = [line[:-1] for line in file]
Note: this last solution only works if the file ends with a newline, otherwise the last line will lose a character.
This assumption is true in most cases (especially for files created by text editors, which often do add an ending newline anyway).
If you want to avoid this you can add a newline at the end of file:
with open(the_file, 'r+') as f:
f.seek(-1, 2) # go at the end of the file
if f.read(1) != '\n':
# add missing newline if not already present
f.write('\n')
f.flush()
f.seek(0)
lines = [line[:-1] for line in f]
Or a simpler alternative is to strip the newline instead:
[line.rstrip('\n') for line in file]
Or even, although pretty unreadable:
[line[:-(line[-1] == '\n') or len(line)+1] for line in file]
Which exploits the fact that the return value of or isn't a boolean, but the object that was evaluated true or false.
The readlines method is actually equivalent to:
def readlines(self):
lines = []
for line in iter(self.readline, ''):
lines.append(line)
return lines
# or equivalently
def readlines(self):
lines = []
while True:
line = self.readline()
if not line:
break
lines.append(line)
return lines
Since readline() keeps the newline also readlines() keeps it.
Note: for symmetry to readlines() the writelines() method does not add ending newlines, so f2.writelines(f.readlines()) produces an exact copy of f in f2.

temp = open(filename,'r').read().split('\n')

Reading file one row at the time. Removing unwanted chars from end of the string with str.rstrip(chars).
with open(filename, 'r') as fileobj:
for row in fileobj:
print(row.rstrip('\n'))
See also str.strip([chars]) and str.lstrip([chars]).

I think this is the best option.
temp = [line.strip() for line in file.readlines()]

temp = open(filename,'r').read().splitlines()

My preferred one-liner -- if you don't count from pathlib import Path :)
lines = Path(filename).read_text().splitlines()
This it auto-closes the file, no need for with open()...
Added in Python 3.5.
https://docs.python.org/3/library/pathlib.html#pathlib.Path.read_text

Try this:
u=open("url.txt","r")
url=u.read().replace('\n','')
print(url)

To get rid of trailing end-of-line (/n) characters and of empty list values (''), try:
f = open(path_sample, "r")
lines = [line.rstrip('\n') for line in f.readlines() if line.strip() != '']

You can read the file as a list easily using a list comprehension
with open("foo.txt", 'r') as f:
lst = [row.rstrip('\n') for row in f]

my_file = open("first_file.txt", "r")
for line in my_file.readlines():
if line[-1:] == "\n":
print(line[:-1])
else:
print(line)
my_file.close()

This script here will take lines from file and save every line without newline with ,0 at the end in file2.
file = open("temp.txt", "+r")
file2 = open("res.txt", "+w")
for line in file:
file2.writelines(f"{line.splitlines()[0]},0\n")
file2.close()
if you looked at line, this value is data\n, so we put splitlines()
to make it as an array and [0] to choose the only word data

import csv
with open(filename) as f:
csvreader = csv.reader(f)
for line in csvreader:
print(line[0])

Appending lines to a file, then reading them

I want to append or write multiple lines to a file. I believe the following code appends one line:
with open(file_path,'a') as file:
file.write('1')
My first question is that if I do this:
with open(file_path,'a') as file:
file.write('1')
file.write('2')
file.write('3')
Will it create a file with the following content?
1
2
3
Second question—if I later do:
with open(file_path,'r') as file:
first = file.read()
second = file.read()
third = file.read()
Will that read the content to the variables so that first will be 1, second will be 2 etc? If not, how do I do it?

Question 1: No.
file.write simple writes whatever you pass to it to the position of the pointer in the file. file.write("Hello "); file.write("World!") will produce a file with contents "Hello World!"
You can write a whole line either by appending a newline character ("\n") to each string to be written, or by using the print function's file keyword argument (which I find to be a bit cleaner)
with open(file_path, 'a') as f:
print('1', file=f)
print('2', file=f)
print('3', file=f)
N.B. print to file doesn't always add a newline, but print itself does by default! print('1', file=f, end='') is identical to f.write('1')
Question 2: No.
file.read() reads the whole file, not one line at a time. In this case you'll get
first == "1\n2\n3"
second == ""
third == ""
This is because after the first call to file.read(), the pointer is set to the end of the file. Subsequent calls try to read from the pointer to the end of the file. Since they're in the same spot, you get an empty string. A better way to do this would be:
with open(file_path, 'r') as f: # `file` is a bad variable name since it shadows the class
lines = f.readlines()
first = lines[0]
second = lines[1]
third = lines[2]
Or:
with open(file_path, 'r') as f:
first, second, third = f.readlines() # fails if there aren't exactly 3 lines

The answer to the first question is no. You're writing individual characters. You would have to read them out individually.
Also, note that file.read() returns the full contents of the file.
If you wrote individual characters and you want to read individual characters, process the result of file.read() as a string.
text = open(file_path).read()
first = text[0]
second = text[1]
third = text[2]
As for the second question, you should write newline characters, '\n', to terminate each line that you write to the file.
with open(file_path, 'w') as out_file:
out_file.write('1\n')
out_file.write('2\n')
out_file.write('3\n')
To read the lines, you can use file.readlines().
lines = open(file_path).readlines()
first = lines[0] # -> '1\n'
second = lines[1] # -> '2\n'
third = lines[2] # -> '3\n'
If you want to get rid of the newline character at the end of each line, use strip(), which discards all whitespace before and after a string. For example:
first = lines[0].strip() # -> '1'
Better yet, you can use map to apply strip() to every line.
lines = list(map(str.strip, open(file_path).readlines()))
first = lines[0] # -> '1'
second = lines[1] # -> '2'
third = lines[2] # -> '3'

Writing multiple lines to a file
This will depend on how the data is stored. For writing individual values, your current example is:
with open(file_path,'a') as file:
file.write('1')
file.write('2')
file.write('3')
The file will contain the following:
123
It will also contain whatever contents it had previously since it was opened to append. To write newlines, you must explicitly add these or use writelines(), which expects an iterable.
Also, I don't recommend using file as an object name since it is a keyword, so I will use f from here on out.
For instance, here is an example where you have a list of values that you write using write() and explicit newline characters:
my_values = ['1', '2', '3']
with open(file_path,'a') as f:
for value in my_values:
f.write(value + '\n')
But a better way would be to use writelines(). To add newlines, you could join them with a list comprehension:
my_values = ['1', '2', '3']
with open(file_path,'a') as f:
f.writelines([value + '\n' for value in my_values])
If you are looking for printing a range of numbers, you could use a for loop with range (or xrange if using Python 2.x and printing a lot of numbers).
Reading individual lines from a file
To read individual lines from a file, you can also use a for loop:
my_list = []
with open(file_path,'r') as f:
for line in f:
my_list.append(line.strip()) # strip out newline characters
This way you can iterate through the lines of the file returned with a for loop (or just process them as you read them, particularly if it's a large file).

Splitting lines in python based on some character

Input:
!,A,56281,12/12/19,19:34:12,000.0,0,37N22.714,121W55.576,+0013!,A,56281,12/1
2/19,19:34:13,000.0,0,37N22.714,121W55.576,+0013!,A,56281,12/12/19,19:34:14,000.
0,0,37N22.714,121W55.576,+0013!,A,56281,12/12/19,19:34:15,000.0,0,37N22.714,121W
55.576,+0013!,A,56281,12/12/19,19:34:16,000.0,0,37N22.714,121W55.576,+0013!,A,56
281,12/12/19,19:34:17,000.0,0,37N22.714,121W55.576,+0013!,A,56281,12/12/19,19:34
:18,000.0,0,37N22.714,121W55.576,+0013!,A,56281,12/12/19,19:34:19,000.0,0,37N22.
Output:
!,A,56281,12/12/19,19:34:12,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:13,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:14,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:15,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:16,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:17,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:18,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:19,000.0,0,37N22.
'!' is the starting character and +0013 should be the ending of each line (if present).
Problem which I am getting:
Output is like :
!,A,56281,12/12/19,19:34:12,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/1
2/19,19:34:13,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:14,000.
0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:15,000.0,0,37N22.714,121W
Any help would be highly appreciated...!!!
My code:
file_open= open('sample.txt','r')
file_read= file_open.read()
file_open2= open('output.txt','w+')
counter =0
for i in file_read:
if '!' in i:
if counter == 1:
file_open2.write('\n')
counter= counter -1
counter= counter +1
file_open2.write(i)

You can try something like this:
with open("abc.txt") as f:
data=f.read().replace("\r\n","") #replace the newlines with ""
#the newline can be "\n" in your system instead of "\r\n"
ans=filter(None,data.split("!")) #split the data at '!', then filter out empty lines
for x in ans:
print "!"+x #or write to some other file
.....:
!,A,56281,12/12/19,19:34:12,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:13,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:14,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:15,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:16,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:17,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:18,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:19,000.0,0,37N22.

Could you just use str.split?
lines = file_read.split('!')
Now lines is a list which holds the split data. This is almost the lines you want to write -- The only difference is that they don't have trailing newlines and they don't have '!' at the start. We can put those in easily with string formatting -- e.g. '!{0}\n'.format(line). Then we can put that whole thing in a generator expression which we'll pass to file.writelines to put the data in a new file:
file_open2.writelines('!{0}\n'.format(line) for line in lines)
You might need:
file_open2.writelines('!{0}\n'.format(line.replace('\n','')) for line in lines)
if you find that you're getting more newlines than you wanted in the output.
A few other points, when opening files, it's nice to use a context manager -- This makes sure that the file is closed properly:
with open('inputfile') as fin:
lines = fin.read()
with open('outputfile','w') as fout:
fout.writelines('!{0}\n'.format(line.replace('\n','')) for line in lines)

Another option, using replace instead of split, since you know the starting and ending characters of each line:
In [14]: data = """!,A,56281,12/12/19,19:34:12,000.0,0,37N22.714,121W55.576,+0013!,A,56281,12/1
2/19,19:34:13,000.0,0,37N22.714,121W55.576,+0013!,A,56281,12/12/19,19:34:14,000.
0,0,37N22.714,121W55.576,+0013!,A,56281,12/12/19,19:34:15,000.0,0,37N22.714,121W
55.576,+0013!,A,56281,12/12/19,19:34:16,000.0,0,37N22.714,121W55.576,+0013!,A,56
281,12/12/19,19:34:17,000.0,0,37N22.714,121W55.576,+0013!,A,56281,12/12/19,19:34
:18,000.0,0,37N22.714,121W55.576,+0013!,A,56281,12/12/19,19:34:19,000.0,0,37N22.""".replace('\n', '')
In [15]: print data.replace('+0013!', "+0013\n!")
!,A,56281,12/12/19,19:34:12,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:13,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:14,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:15,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:16,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:17,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:18,000.0,0,37N22.714,121W55.576,+0013
!,A,56281,12/12/19,19:34:19,000.0,0,37N22.

Just for some variance, here is a regular expression answer:
import re
outputFile = open('output.txt', 'w+')
with open('sample.txt', 'r') as f:
for line in re.findall("!.+?(?=!|$)", f.read(), re.DOTALL):
outputFile.write(line.replace("\n", "") + '\n')
outputFile.close()
It will open the output file, get the contents of the input file, and loop through all the matches using the regular expression !.+?(?=!|$) with the re.DOTALL flag. The regular expression explanation & what it matches can be found here: http://regex101.com/r/aK6aV4
After we have a match, we strip out the new lines from the match, and write it to the file.

Let's try to add a \n before every "!"; then let python splitlines :-) :
file_read.replace("!", "!\n").splitlines()

I will actually implement as a generator so that you can work on the data stream rather than the entire content of the file. This will be quite memory friendly if working with huge files
>>> def split_on_stream(it,sep="!"):
prev = ""
for line in it:
line = (prev + line.strip()).split(sep)
for parts in line[:-1]:
yield parts
prev = line[-1]
yield prev
>>> with open("test.txt") as fin:
for parts in split_on_stream(fin):
print parts
,A,56281,12/12/19,19:34:12,000.0,0,37N22.714,121W55.576,+0013
,A,56281,12/12/19,19:34:13,000.0,0,37N22.714,121W55.576,+0013
,A,56281,12/12/19,19:34:14,000.0,0,37N22.714,121W55.576,+0013
,A,56281,12/12/19,19:34:15,000.0,0,37N22.714,121W55.576,+0013
,A,56281,12/12/19,19:34:16,000.0,0,37N22.714,121W55.576,+0013
,A,56281,12/12/19,19:34:17,000.0,0,37N22.714,121W55.576,+0013
,A,56281,12/12/19,19:34:18,000.0,0,37N22.714,121W55.576,+0013
,A,56281,12/12/19,19:34:19,000.0,0,37N22.