Python: Replacing a string with unique replacements

Question

I'm reading a file and I need to replace certain empty tags ([[Image:]]).

The problem is every replacement has to be unique.

Here's the code:

import re
import codecs

re_imagematch = re.compile('(\[\[Image:([^\]]+)?\]\])')

wf = codecs.open('converted.wiki', "r", "utf-8")
wikilines = wf.readlines()
wf.close()

imgidx = 0
for i in range(0,len(wikilines)):
 if re_imagematch.search(wikilines[i]):
  print 'MATCH #######################################################'
  print wikilines[i]
  wikilines[i] = re_imagematch.sub('[[Image:%s_%s.%s]]' % ('outname', imgidx, 'extension'), wikilines[i])
  print wikilines[i]
  imgidx += 1

This does not work, as there can be many tags in one line:

Here's the input file.

[[Image:]][[Image:]]
[[Image:]]

This is what the output should look like:

[[Image:outname_0.extension]][Image:outname_1.extension]]
[[Image:outname_2.extension]]

This is what it currently looks likeö

[[Image:outname_0.extension]][Image:outname_0.extension]]
[[Image:outname_1.extension]]

I tried using a replacement function, the problem is this function gets only called once per line using re.sub.

Community · Accepted Answer · 2017-05-23 10:33:32Z

3

You can use itertools.count here and take some advantage of the fact that default arguments are calculated when function is created and value of mutable default arguments can persist between function calls.

from itertools import count

def rep(m, cnt=count()):
    return '[[Image:%s_%s.%s]]' % ('outname', next(cnt) , 'extension')

This function will be invoked for each match found and it'll use a new value for each replacement.

So, you simply need to change this line in your code:

wikilines[i] = re_imagematch.sub(rep, wikilines[i])

Demo:

def rep(m, count=count()):
    return str(next(count))

>>> re.sub(r'a', rep, 'aaa')
'012'

To get the current counter value:

>>> from copy import copy
>>> next(copy(rep.__defaults__[0])) - 1
2

edited May 23, 2017 at 10:33

CommunityBot

11 silver badge

answered Aug 10, 2014 at 17:33

Ashwini Chaudhary

252k60 gold badges478 silver badges519 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Jon Clements Over a year ago

@AshwiniChaudhary although the current counter value works, it might be easier to wrap in a class that exposes a property of the previously yielded value... Although - it's quite a bit more work :p

Falko · Accepted Answer · 2014-08-10 17:40:15Z

1

I'd use a simple string replacement wrapped in a while loop:

s = '[[Image:]][[Image:]]\n[[Image:]]'
pattern = '[[Image:]]'
i = 0
while s.find(pattern) >= 0:
    s = s.replace(pattern, '[[Image:outname_' + str(i) + '.extension]]', 1)
    i += 1
print s

answered Aug 10, 2014 at 17:40

Falko

18.2k14 gold badges65 silver badges119 bronze badges

1 Comment

Marki Over a year ago

Since I'm not a big expert in Python, and neither are the people here that have to understand this too, I am accepting your answer. Thanks.

Collectives™ on Stack Overflow

Python: Replacing a string with unique replacements

2 Answers 2

1 Comment

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related