Need to delete part of text lines in python

I have the following problem. I have a list of different text lines that all has a comma in it. I want to keep the text to the left of the comma and delete everything that occurs after the comma for all the lines in the file.

Here is a sample line from the file:

1780375 "004956 , down , 943794 , 22634 , ET , 2115 ,

I'd like to delete the characters after the first comma:

I tried to make the program yet am having some trouble. Here is what i have so far:

datafile = open('C:\\middlelist3.txt', 'r')

smallerdataset = open('C:\\nocommas.txt', 'w')

counter = 1

for line in datafile:
    print counter
    counter +=1
    datafile.rstrip(s[,])
    smallerdata开发者_StackOverflow中文版set.write(line)

You can use split for this. It splits the string on a given substring. As you only need the first part, I set 1 as the second parameter to make it only split on the first one.

Instead of using a counter, you could use enumerate, like this:

datafile = open('C:\\middlelist3.txt', 'r')

smallerdataset = open('C:\\nocommas.txt', 'w')

for counter, line in enumerate(datafile):
    print counter
    smallerdataset.write(line.split(',', 1)[0])   

smallerdataset.close()

This is how you could improve your script using the with statement and generator expressions:

with open('C:\\middlelist3.txt') as datafile:
    list = (line.split(',', 1)[0] for line in datafile)
    with open('C:\\nocommas.txt', 'w') as smallfile:
        smallfile.writelines(list)