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Groups > comp.lang.python > #99702

Re: I can't understand re.sub

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On Sun, 29 Nov 2015 13:36:57 -0800, Mr Zaug wrote:

> result = re.sub(pattern, repl, string, count=0, flags=0);

re.sub works on a string, not on a file.

Read the file to a string, pass it in as the string.

Or pre-compile the search pattern(s) and process the file line by line:

import re

patts = [
 (re.compile("axe"), "hammer"),
 (re.compile("cat"), "dog"),
 (re.compile("tree"), "fence")
 ]

with open("input.txt","r") as inf, open("output.txt","w") as ouf:
    line = inf.readline()
    for patt in patts:
        line = patt[0].sub(patt[1], line)
    ouf.write(line)

Not tested, but I think it should do the trick.

Or use a single patt and a replacement func:

import re

patt = re.compile("(axe)|(cat)|(tree)")

def replfunc(match):
    if match == 'axe':
        return 'hammer'
    if match == 'cat':
        return 'dog'
    if match == 'tree':
        return 'fence'
    return match

with open("input.txt","r") as inf, open("output.txt","w") as ouf:
    line = inf.readline()
    line = patt.sub(replfunc, line)
    ouf.write(line)

(also not tested)

-- 
Denis McMahon, denismfmcmahon@gmail.com

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Thread

I can't understand re.sub Mr Zaug <matthew.herzog@gmail.com> - 2015-11-29 13:36 -0800
  Re: I can't understand re.sub Denis McMahon <denismfmcmahon@gmail.com> - 2015-11-29 22:01 +0000
    Re: I can't understand re.sub Mr Zaug <matthew.herzog@gmail.com> - 2015-11-29 17:20 -0800
  Re: I can't understand re.sub Rick Johnson <rantingrickjohnson@gmail.com> - 2015-11-29 17:12 -0800
    Re: I can't understand re.sub Mr Zaug <matthew.herzog@gmail.com> - 2015-11-29 17:24 -0800
  Re: I can't understand re.sub Erik <python@lucidity.plus.com> - 2015-11-29 21:53 +0000
    Re: I can't understand re.sub Jussi Piitulainen <harvesting@is.invalid> - 2015-11-30 10:51 +0200
      Re: I can't understand re.sub Erik <python@lucidity.plus.com> - 2015-12-01 01:26 +0000
        Re: I can't understand re.sub Jussi Piitulainen <harvesting@is.invalid> - 2015-12-01 07:28 +0200
          Re: I can't understand re.sub Erik <python@lucidity.plus.com> - 2015-12-01 21:31 +0000

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