Python string replacement with random items

Question

String replacement in Python is not difficult, but I want to do something special:

teststr = 'test test test test'
animals = ['bird','monkey','dog','fox']
#replace 'test' with random item from animals
finalstr = ['dog fox dog monkey']

I write a very inefficient version:

from random import choice
import string
import re

teststr = 'test test test test'
animals = ['bird','monkey','dog','fox']

indexes = [m.start() for m in re.finditer('test', 'test test test test')]
#indexes = [0, 5, 10, 15]
for i in indexes:
    string.replace(teststr, 'test', choice(animals), 1)

#Final result is four random animals
#maybe ['dog fox dog monkey']

It works, but I believe there is some simple method with REGULAR EXPRESSION which I am not familiar with.

unutbu · Accepted Answer · 2012-09-16 18:42:39Z

13

Use a re.sub callback:

import re
import random

animals = ['bird','monkey','dog','fox']

def callback(matchobj):
    return random.choice(animals)

teststr = 'test test test test'
ret = re.sub(r'test', callback, teststr)
print(ret)

yields (for example)

bird bird dog monkey

The second argument to re.sub can be a string or a function (i.e. a callback). If it is a function, it is called for every non-overlapping occurrance of the regex pattern, and its return value is substituted in place of the matched string.

answered Sep 16, 2012 at 18:42

unutbu

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2 Comments

Gaby Solis Over a year ago

I dont know who delete the "lambda" verson: re.sub(r'test', lambda m: random.choice(animals), teststr) Actually it seems to be more succinct.

sloth Over a year ago

@GabySolis I deleted it (it was my answer). I thought the answer was unneccesary since unutbu already answered your question some seconds before me, basically saying the same: use re.sub with a callback. But if you like it, I undelete my answer.

sloth · Accepted Answer · 2012-09-16 18:44:11Z

1

You can use re.sub:

>>> from random import choice
>>> import re
>>> teststr = 'test test test test'
>>> animals = ['bird','monkey','dog','fox']
>>> re.sub('test', lambda m: choice(animals), teststr)
'fox monkey bird dog'
>>> re.sub('test', lambda m: choice(animals), teststr)
'fox dog dog bird'
>>> re.sub('test', lambda m: choice(animals), teststr)
'monkey bird monkey monkey'

answered Sep 16, 2012 at 18:44

sloth

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Comments

Bleeding Fingers · Accepted Answer · 2012-09-16 19:05:21Z

1

This would do the job:

import random, re
def rand_replacement(string, to_be_replaced, items):
    return re.sub(to_be_replaced, lambda x: random.choice(items), string )

answered Sep 16, 2012 at 19:05

Bleeding Fingers

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