How to replace multiple substrings of a string?


Question

I would like to use the .replace function to replace multiple strings.

I currently have

string.replace("condition1", "")

but would like to have something like

string.replace("condition1", "").replace("condition2", "text")

although that does not feel like good syntax

what is the proper way to do this? kind of like how in grep/regex you can do \1 and \2 to replace fields to certain search strings

1
235
12/8/2017 4:57:01 PM

Accepted Answer

Here is a short example that should do the trick with regular expressions:

import re

rep = {"condition1": "", "condition2": "text"} # define desired replacements here

# use these three lines to do the replacement
rep = dict((re.escape(k), v) for k, v in rep.iteritems()) 
#Python 3 renamed dict.iteritems to dict.items so use rep.items() for latest versions
pattern = re.compile("|".join(rep.keys()))
text = pattern.sub(lambda m: rep[re.escape(m.group(0))], text)

For example:

>>> pattern.sub(lambda m: rep[re.escape(m.group(0))], "(condition1) and --condition2--")
'() and --text--'
234
5/22/2019 9:55:53 AM

You could just make a nice little looping function.

def replace_all(text, dic):
    for i, j in dic.iteritems():
        text = text.replace(i, j)
    return text

where text is the complete string and dic is a dictionary — each definition is a string that will replace a match to the term.

Note: in Python 3, iteritems() has been replaced with items()


Careful: Python dictionaries don't have a reliable order for iteration. This solution only solves your problem if:

  • order of replacements is irrelevant
  • it's ok for a replacement to change the results of previous replacements

For instance:

d = { "cat": "dog", "dog": "pig"}
mySentence = "This is my cat and this is my dog."
replace_all(mySentence, d)
print(mySentence)

Possible output #1:

"This is my pig and this is my pig."

Possible output #2

"This is my dog and this is my pig."

One possible fix is to use an OrderedDict.

from collections import OrderedDict
def replace_all(text, dic):
    for i, j in dic.items():
        text = text.replace(i, j)
    return text
od = OrderedDict([("cat", "dog"), ("dog", "pig")])
mySentence = "This is my cat and this is my dog."
replace_all(mySentence, od)
print(mySentence)

Output:

"This is my pig and this is my pig."

Careful #2: Inefficient if your text string is too big or there are many pairs in the dictionary.


Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow
Icon