Modify file using python

Question

I have files that contains the following lines:

info face="asd" size=49 bold=0 italic=0 charset="" unicode=0 stretchH=100 smooth=1 aa=1 padding=0,0,0,0 spacing=0,0
common lineHeight=52 base=43 scaleW=128 scaleH=128 pages=1 packed=0
page id=0 file="asd.png"
chars count=9
char id=32 x=58 y=82 width=0 height=0 xoffset=0 yoffset=40 xadvance=9 page=0 chnl=0
char id=179 x=34 y=42 width=28 height=38 xoffset=2 yoffset=6 xadvance=26 page=0 chnl=0
char id=181 x=94 y=2 width=28 height=38 xoffset=2 yoffset=6 xadvance=26 page=0 chnl=0
char id=183 x=2 y=42 width=30 height=38 xoffset=2 yoffset=6 xadvance=27 page=0 chnl=0
char id=185 x=2 y=2 width=30 height=38 xoffset=2 yoffset=6 xadvance=27 page=0 chnl=0
char id=187 x=64 y=2 width=28 height=38 xoffset=2 yoffset=6 xadvance=26 page=0 chnl=0
char id=189 x=34 y=2 width=28 height=38 xoffset=2 yoffset=6 xadvance=26 page=0 chnl=0
char id=191 x=34 y=82 width=22 height=36 xoffset=2 yoffset=8 xadvance=18 page=0 chnl=0
char id=193 x=2 y=82 width=28 height=38 xoffset=2 yoffset=6 xadvance=26 page=0 chnl=0
kernings count=0

I need to find the id value, then based on simple condition modify(add/subtract some number from the value) that number and write file back. My attempt is:

input = open('file.txt', 'r')
for line in input:

here I am thinking to capture 3 parts of line char id=, value and the rest of line. Then modify value and create new string. But I doubt it's effective way in Python. Also I'm not sure if there is a way to work on same file instead of creating new file, deleting old and renaming back to old name in order to modify file content.

" I'm not sure if there is a way to work on same file instead of creating new file, deleting old and renaming back to old name" Yes, there is, but the condition is that every part of string that must be replaced must be longer or of same length than the replacement one. An example of this way to process here: (stackoverflow.com/a/16591889/551449) The key is to open the file in mode 'rb+'. But the example I give is rather complex because in this file it was possible that the pattern to be replaced would be contiguously repeated. In your case, it wouldn't be the case, I presume. — eyquem
– eyquem, Commented May 22, 2013 at 22:04

Martijn Pieters · Accepted Answer · 2013-05-22 21:34:35Z

4

You'll have to replace the file (so write to a temporary file). However, the fileinput module makes this easy for you:

import fileinput
import sys

for line in fileinput.input(filename, inplace=True):
    if line.startswith('char id='):
        _, id_, rest = line.split(None, 2)
        id_ = int(id_.split('=')[1])
        id_ += 1  # adjust as needed
        line = 'char id={} {}'.format(id_, rest)

    sys.stdout.write(line)

This example simply increments the id value by 1, you can adjust the code to do whatever you want with the id_ integer.

By specifying inplace=True, the fileinput module will move the original file to a backup, capture anything you write to stdout, and write it to original file location instead.

edited May 22, 2013 at 21:34

answered May 22, 2013 at 21:25

Martijn Pieters

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3 Comments

Pablo Over a year ago

I got invalid syntax on id_. Is this some reserved keyword?

Martijn Pieters Over a year ago

@Pablo: No, I forgot to remove some text (int() on the previous line as I edited the answer. Fixed.

Pablo Over a year ago

works like a charm, just had to .close stream otherwise the file was empty. thanks!

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