I am very new to programming and the python language.
I know how to open a file in python, but the question is how can I open the file as a parameter of a function?
example:
function(parameter)
Here is how I have written out the code:
def function(file):
with open('file.txt', 'r') as f:
contents = f.readlines()
lines = []
for line in f:
lines.append(line)
print(contents)
You can easily pass the file object.
with open('file.txt', 'r') as f: #open the file
contents = function(f) #put the lines to a variable.
and in your function, return the list of lines
def function(file):
lines = []
for line in f:
lines.append(line)
return lines
Another trick, python file objects actually have a method to read the lines of the file. Like this:
with open('file.txt', 'r') as f: #open the file
contents = f.readlines() #put the lines to a variable (list).
With the second method, readlines is like your function. You don't have to call it again.
Update
Here is how you should write your code:
First method:
def function(file):
lines = []
for line in f:
lines.append(line)
return lines
with open('file.txt', 'r') as f: #open the file
contents = function(f) #put the lines to a variable (list).
print(contents)
Second one:
with open('file.txt', 'r') as f: #open the file
contents = f.readlines() #put the lines to a variable (list).
print(contents)
Hope this helps!
Python allows to put multiple open() statements in a single with. You comma-separate them. Your code would then be:
def filter(txt, oldfile, newfile):
'''\
Read a list of names from a file line by line into an output file.
If a line begins with a particular name, insert a string of text
after the name before appending the line to the output file.
'''
with open(newfile, 'w') as outfile, open(oldfile, 'r', encoding='utf-8') as infile:
for line in infile:
if line.startswith(txt):
line = line[0:len(txt)] + ' - Truly a great person!\n'
outfile.write(line)
# input the name you want to check against
text = input('Please enter the name of a great person: ')
letsgo = filter(text,'Spanish', 'Spanish2')
And no, you don't gain anything by putting an explicit return at the end of your function. You can use return to exit early, but you had it at the end, and the function will exit without it. (Of course with functions that return a value, you use the return to specify the value to return.)
def fun(file):
contents = None
with open(file, 'r') as fp:
contents = fp.readlines()
## if you want to eliminate all blank lines uncomment the next line
#contents = [line for line in ''.join(contents).splitlines() if line]
return contents
print fun('test_file.txt')
or you can even modify this, such a way it takes file object as a function arguement as well
Here's a much simpler way of opening a file without defining your own function in Python 3.4:
var=open("A_blank_text_document_you_created","type_of_file")
var.write("what you want to write")
print (var.read()) #this outputs the file contents
var.close() #closing the file
Here are the types of files:
"r": just to read a file
"w": just to write a file
"r+": a special type which allows both reading and writing of the file
For more information see this cheatsheet.
def main():
file=open("chirag.txt","r")
for n in file:
print (n.strip("t"))
file.close()
if __name__== "__main__":
main()
the other method is
with open("chirag.txt","r") as f:
for n in f:
print(n)
Related
I have a huge list of python packages that had been installed saved with the version numbers in the file "foo.txt", I want to delete the "==" and whatever after that in each lines, and save the file.
example text in the file:
autopep8==1.5.3
beautifulsoup4==4.8.2
bleach==3.1.4
bumpversion==0.5.3
... etc
Use this line of code if you want to create a new file with updated data, if you want to just read use the data then make changes accordingly.
def read_write_file(input_path, output_path):
with open(input_path, "r") as input_file:
content = input_file.readlines()
with open(output_path, 'w') as output_file:
for line in content:
line = line[:line.find('==')]
output_file.write(line + '\n')
Use the below code.
read that file and store it in list named pkg_list.
output_lst = []
with open("input.txt", "r") as f:
input_data = f.readlines()
output_lst = [name.split("==")[0] for name in input_data]
with open("input.txt", "w") as f:
for pkg in output_lst:
f.write("{}\n".format(pkg))
I would like to read a file line by line but ignore any that contain a colon (:).
I'm currently opening one file, reading it, and trying to print it before eventually put it into a new file.
def shoppinglist():
infile = open('filename.txt')
contents = infile.readline()
output = open('outputfilename.txt', 'w')
while ":" not in contents:
contents = infile.readline()
else:
contentstr = contents.split()
print(contentstr)
output.write(contents)
infile.close()
output.close()
As it is, one line is repeated over and over and over.
Try:
def shoppinglist():
contents = ""
with open('filename.txt', 'r') as infile:
for line in infile.readlines():
if ":" not in line:
contents += line
with open('outputfilename.txt', 'w') as output_file:
output_file.write(contents)
Output:
Sorry, this was being awfully awkward when I trying to paste my Python code into the code box on this forum post.
Code:
# update three quotes to a file
file_name = "my_quote.txt"
# create a file called my_quote.txt
new_file = open(file_name, 'w')
new_file.close()
def update_file(file_name, quote):
# First open the file
new_file = open(file_name, 'w')
new_file.write("This is an update\n")
new_file.write(quote)
new_file.write("\n\n")
# now close the file
new_file.close()
for index in range(3):
quote = input("Enter your favorite quote: ")
update_file(file_name, quote)
# Now print the contents to the screen
new_file = open(file_name, 'r')
print(new_file.read())
# And finally close the file
new_file.close(
You should be using append instead of write. When you use write, it creates a new file regardless of what was there before. Try new_file = open(file_name, 'a')
Why is it only writing last input to txt?
Everytime you do open(file_name, 'w') it clears the contents of the file and begins to write from the start of the file.
If you would like to append new content to that file do
open(file_name, 'a')
I guess you should use a instead of w to append to file:
new_file = open(file_name, 'a')
And read the docs before asking of course ;)
Currently I'm using this:
f = open(filename, 'r+')
text = f.read()
text = re.sub('foobar', 'bar', text)
f.seek(0)
f.write(text)
f.close()
But the problem is that the old file is larger than the new file. So I end up with a new file that has a part of the old file on the end of it.
If you don't want to close and reopen the file, to avoid race conditions, you could truncate it:
f = open(filename, 'r+')
text = f.read()
text = re.sub('foobar', 'bar', text)
f.seek(0)
f.write(text)
f.truncate()
f.close()
The functionality will likely also be cleaner and safer using open as a context manager, which will close the file handler, even if an error occurs!
with open(filename, 'r+') as f:
text = f.read()
text = re.sub('foobar', 'bar', text)
f.seek(0)
f.write(text)
f.truncate()
The fileinput module has an inplace mode for writing changes to the file you are processing without using temporary files etc. The module nicely encapsulates the common operation of looping over the lines in a list of files, via an object which transparently keeps track of the file name, line number etc if you should want to inspect them inside the loop.
from fileinput import FileInput
for line in FileInput("file", inplace=1):
line = line.replace("foobar", "bar")
print(line)
Probably it would be easier and neater to close the file after text = re.sub('foobar', 'bar', text), re-open it for writing (thus clearing old contents), and write your updated text to it.
I find it easier to remember to just read it and then write it.
For example:
with open('file') as f:
data = f.read()
with open('file', 'w') as f:
f.write('hello')
To anyone who wants to read and overwrite by line, refer to this answer.
https://stackoverflow.com/a/71285415/11442980
filename = input("Enter filename: ")
with open(filename, 'r+') as file:
lines = file.readlines()
file.seek(0)
for line in lines:
value = int(line)
file.write(str(value + 1))
file.truncate()
Honestly you can take a look at this class that I built which does basic file operations. The write method overwrites and append keeps old data.
class IO:
def read(self, filename):
toRead = open(filename, "rb")
out = toRead.read()
toRead.close()
return out
def write(self, filename, data):
toWrite = open(filename, "wb")
out = toWrite.write(data)
toWrite.close()
def append(self, filename, data):
append = self.read(filename)
self.write(filename, append+data)
Try writing it in a new file..
f = open(filename, 'r+')
f2= open(filename2,'a+')
text = f.read()
text = re.sub('foobar', 'bar', text)
f.seek(0)
f.close()
f2.write(text)
fw.close()
imp,2,6,7
ads,4,5,6
sfd,2,5,8
I have a text file that looks like this
I want to delete the line that has imp in it.
All the other methods I have seen to delete lines from files only work for single strings
Following this question link, you can try this:
fn = 'Test.txt'
f = open(fn)
output = []
for line in f:
if not "imp" in line:
output.append(line)
f.close()
f = open(fn, 'w')
f.writelines(output)
f.close()
Result:
ads,4,5,6
sfd,2,5,8