Changing a file line - Python

Question

I've a file entitled 'users.txt' with the following structure; username:info_about_the_user.

Something like this:

users.txt:

mark:stuffabouthim
anthony:stuffabouthim
peter:stuffabouthim
peterpeter:stuffabouthim
peterpeterpeter:stuffabouthim
peterpeterpeterpeter:stuffabouthim

The following part of the script needs to change a line (change info about an user) but I'm having problems when the string is duplicated (peter - peterpeter) and I dont know how to fix it.

def test():
    fn = 'users.txt'
    f = open(fn)
    output = []
    changeuser = 'peterpeter'
    userinfo = 'HeIsTall'
    for line in f:
        if not changeuser+":" in line:
            output.append(line)
    f.close()
    f = open(fn, 'w')
    f.writelines(output)
    f.close()
    f = open("users.txt", "a")
    f.write(changeuser + ":" + userinfo+"\n")
    f = open("users.txt", "a")

test()

This is the input I have:

Input: users.txt:

mark:stuffabouthim
anthony:stuffabouthim
peter:stuffabouthim
peterpeter:HesAwesome
peterpeterpeter:stuffabouthim
peterpeterpeterpeter:stuffabouthim

I want to change info about peterpeter and have the following output:

Output I want to have: users.txt:

mark:stuffabouthim
anthony:stuff about him
peter:stuffabouthim
peterpeter:HeIsTall
peterpeterpeter:stuffabouthim
peterpeterpeterpeter:stuffabouthim

But this is the input I'm having. All the lines behind peterpeter are getting deleted among other things.

mark:stuffabouthim
anthony:stuffabouthim
peter:stuffabouthim
peterpeter:HeIsTall

Can anyone give me a help with the code below to have the desired output? Thanks.

Do you really need python for this? You might be better off with awk + sed linux commands. — Mihai Oprea
– Mihai Oprea, Commented Jul 6, 2012 at 9:57
and if he would want to do it in assembler he would have a reason to do so - btw. it almost certainly looks like homework to me! ;-) — Don Question
– Don Question, Commented Jul 7, 2012 at 22:36

sloth · Accepted Answer · 2012-07-06 09:55:42Z

3

You can have it the easy way with the fileinput module:

import fileinput

def test():
    fn = 'users.txt'

    changeuser = 'peterpeter'
    newinfo = 'HeIsTall'

    for line in fileinput.input(fn, inplace=1):
        user, oldinfo = line.split(':')
        print '%s:%s' % (user, newinfo if user == changeuser else oldinfo.replace('\n', ''))

if __name__ == "__main__":
    test()

answered Jul 6, 2012 at 9:55

sloth

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Ashwini Chaudhary · Accepted Answer · 2012-07-06 09:44:13Z

2

try this:

def test():
    fn = 'users.txt.txt'
    f = open(fn)
    output = []
    changeuser = 'peterpeter'
    userinfo = 'HeIsTall'
    for line in f:
        if line.strip().split(':')[0]!=changeuser:
            output.append(line)
        else:
            output.append(changeuser + ":" + userinfo+"\n")

    f.close()
    f = open(fn, 'w')
    f.writelines(output)
    f.close()

test()

output:

mark:stuffabouthim
anthony:stuffabouthim
peter:stuffabouthim
peterpeter:HeIsTall
peterpeterpeter:stuffabouthim
peterpeterpeterpeter:stuffabouthim

edited Jul 6, 2012 at 9:44

answered Jul 6, 2012 at 9:36

Ashwini Chaudhary

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1 Comment

Avión Over a year ago

It's mostly ok, but that appends it on the last line. like this: peterpeterpeterpeter:stuffabouthimpeterpeter:HeIsTall Do you know how to put them in different lines?

Don Question · Accepted Answer · 2012-07-06 11:52:14Z

You got a logical error in the if-clause, which DELETES all peters*, the only peter remaining is the one you append to the file.

for line in f:
        if not changeuser+":" in line:  #THAT MEANS ALL PETERS ARE IGNORED!
            output.append(line)

It's generaly easier to understand positive clauses then a negation:

for line in f:
   if changeuser+":" in line:
      output.append('%s:%s\n' %(changeuser,userinfo))
   else:
      output.append(line)

Good code is easy to read. Try to code like you would try to write a report! That leads automatically to spliting your code into smaller pieces like functions. e.g.:

lines = read_all_lines_from_file(filename)
change_user_info(lines, user, userinfo)
save_lines_to_file(lines, filename)

Your code gets split into smaller pieces and if an error occurs you can pin it down to a few lines of code instead of having to work over several pages. ;-)

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