replace same pattern with different replace value

Question

I have a file like this (this is a simplified version):

james sfsf qef qef
qef qef qe fff
qqew james james qef
qefq ffgrsf wsef 
qef james eq james

I want to replace each iteration of 'james' with a different value. Here's what I have in my test code:

f=open('file_to_be_read.txt','r')
text=f.read()
matches=len(re.findall('james',text))
f.close()
number=0
for x in range(matches):
    new_text=re.sub(r'james',str(number),text,count=1)
    number+=1
r=open('result_file.txt','w')
r.write(new_text)
r.close()

But it just replaces the first 'james' with 2. Rather than produce the following result that I want:

1 sfsf qef qef
qef qef qe fff
qqew 2 3 qef
qefq ffgrsf wsef 
qef 4 eq 5

I thought that by repeating the re.sub with count=1 I would replace 1 james each time but allow me to change the replace value.

"But it just replaces the first 'james' with 2". Strange. It replaces it with "4" on my machine. — Kevin
– Kevin, Commented Aug 24, 2015 at 12:43
You're right, in typing it up I changed my example file I was reading from. — TaxpayersMoney
– TaxpayersMoney, Commented Aug 24, 2015 at 12:51

Ashwini Chaudhary · Accepted Answer · 2015-08-24 12:46:48Z

6

I would recommend using itertools.count for this:

>>> from itertools import count
>>> import re
>>> s = '''james sfsf qef qef
qef qef qe fff
qqew james james qef
qefq ffgrsf wsef
qef james eq james'''
>>> print re.sub(r'james', lambda x, c=count(1): str(next(c)), s)
1 sfsf qef qef
qef qef qe fff
qqew 2 3 qef
qefq ffgrsf wsef
qef 4 eq 5

Here c=count(1) is a default argument value and it is going to be calculated only once(when the function object is created), next calls to this function are going to increment the previous count each time.

answered Aug 24, 2015 at 12:46

Ashwini Chaudhary

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1 Comment

TaxpayersMoney Over a year ago

Thanks. I accepted another one because it was closer to the way I was doing it, but it's always nice to see more efficient solutions too.

scytale · Accepted Answer · 2015-08-24 12:44:14Z

2

you're discarding the updated string - try this:

text = re.sub(r'james', str(x), text, count=1)

answered Aug 24, 2015 at 12:44

scytale

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1 Comment

TaxpayersMoney Over a year ago

Thanks, that was a silly mistake by me. Sometimes I can't see the wood for the trees.

dsh · Accepted Answer · 2015-08-24 12:46:57Z

0

new_text=re.sub(r'james',str(number),text,count=1)

You are working on text each time. You give it the same input text to work with, rather than processing your new_text.

Try this:

new_text = text
for x in range(matches):
    new_text=re.sub(r'james',str(number),new_text,count=1)
    number+=1
number+=1

answered Aug 24, 2015 at 12:46

dsh

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Comments

Wolf · Accepted Answer · 2015-08-24 12:54:08Z

0

re.sub can take a function as the replacement value. This does roughly what you want

import re

with open('file_to_be_read.txt', 'r') as f:
    text = f.read()

number = 0
def do_replace( matchobj ):
    global number
    replacement = str(number)
    number += 1
    return replacement

new_text = re.sub(r'james', do_replace, text)

with open('result_file.txt', 'w') as r:
    r.write(new_text)

answered Aug 24, 2015 at 12:54

Wolf

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