How to remove specific substrings from a set of strings in Python?

python python-3.x
controlfreak picture controlfreak · May 22, 2016 · Viewed 417k times · Source

I have a set of strings set1, and all the strings in set1 have a two specific substrings which I don't need and want to remove.
Sample Input: set1={'Apple.good','Orange.good','Pear.bad','Pear.good','Banana.bad','Potato.bad'}
So basically I want the .good and .bad substrings removed from all the strings.
What I tried:

for x in set1:
    x.replace('.good','')
    x.replace('.bad','')

But this doesn't seem to work at all. There is absolutely no change in the output and it is the same as the input. I tried using for x in list(set1) instead of the original one but that doesn't change anything.

Answer

Reut Sharabani picture Reut Sharabani · May 22, 2016

Strings are immutable. string.replace (python 2.x) or str.replace (python 3.x) creates a new string. This is stated in the documentation:

Return a copy of string s with all occurrences of substring old replaced by new. ...

This means you have to re-allocate the set or re-populate it (re-allocating is easier with set comprehension):

new_set = {x.replace('.good', '').replace('.bad', '') for x in set1}

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