Python Case Insensitive Replace All of multiple strings

Question

I want to replace all occurrences of a set of strings in a text line. I came up with this approach, but I am sure there is a better way of doing this:

myDict = {}
test = re.compile(re.escape('pig'), re.IGNORECASE)
myDict['car'] = test
test = re.compile(re.escape('horse'), re.IGNORECASE)
myDict['airplane'] = test
test = re.compile(re.escape('cow'), re.IGNORECASE)
myDict['bus'] = test

mystring = 'I have this Pig and that pig with a hOrse and coW'

for key in myDict:      
    regex_obj = myDict[key]
    mystring = regex_obj.sub(key, mystring)

print mystring

I have this car and that car with a airplane and bus

Based on @Paul Rooney's answer below, ideally I would do this:

def init_regex():
    rd = {'pig': 'car', 'horse':'airplane', 'cow':'bus'}
    myDict = {}
    for key,value in rd.iteritems():
        pattern = re.compile(re.escape(key), re.IGNORECASE)
        myDict[value] = pattern

    return myDict

def strrep(mystring, patternDict):
    for key in patternDict:
        regex_obj = patternDict[key]
        mystring = regex_obj.sub(key, mystring)

    return mystring

I am not sure there is anything significantly better than this. See stackoverflow.com/questions/919056/… — nullstellensatz
– nullstellensatz, Commented Mar 25, 2015 at 0:08

Paul Rooney · Accepted Answer · 2020-05-01 11:05:17Z

4

Try

import itertools
import re

mystring = 'I have this Pig and that pig with a hOrse and coW'

rd = {'pig': 'car', 'horse':'airplane', 'cow':'bus'}

cachedict = {}

def strrep(orig, repdict):
    for k,v in repdict.iteritems():
        if k in cachedict:
            pattern = cachedict[k]
        else:
            pattern = re.compile(k, re.IGNORECASE)
            cachedict[k] = pattern
        orig = pattern.sub(v, orig)
    return orig

print strrep(mystring, rd)

This answer was initially written for python2, but for python 3 you would use repdict.items instead of repdict.iteritems.

edited May 1, 2020 at 11:05

answered Mar 25, 2015 at 0:09

Paul Rooney

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7 Comments

Amro Younes Over a year ago

Is it possible to cache the compile to save on computation as my strrep would be called multiple times?

Amro Younes Over a year ago

Based on your answer I improved the solution to cache the compiled portion of the code into an array so I don't have to do this everytime and then just call the patter with .sub

Paul Rooney Over a year ago

Yes that works. I was looking at a solution to cache the compiled regex's into a dict.

Paul Rooney Over a year ago

The dict caching solution seems to actually be a bit slower than without the caching.

Amro Younes Over a year ago

The reason your approach to a dictionary degrades performance is probably because you specify a default if the key is not found. I would venture to guess that python performs the compile before calling the get which causes the additional compute unnecessarily every time.

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