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.

9 Answers

Strings are immutable. str.replace creates a new string. This is stated in the documentation:

str.replace(old, new[, count])

Return a copy of the string 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 a set comprehension):

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

NOTE: If you intend to change prefix or suffix str.removeprefix('prefix') str.removesuffix('suffix') respectively should be used.

>>> x = 'Pear.good' >>> y = x.replace('.good','') >>> y 'Pear' >>> x 'Pear.good' 

.replace doesn't change the string, it returns a copy of the string with the replacement. You can't change the string directly because strings are immutable.

You need to take the return values from x.replace and put them in a new set.

In Python 3.9+ you could remove the suffix using str.removesuffix('mysuffix'). From the docs:

If the string ends with the suffix string and that suffix is not empty, return string[:-len(suffix)]. Otherwise, return a copy of the original string

So you can either create a new empty set and add each element without the suffix to it:

set1 = {'Apple.good', 'Orange.good', 'Pear.bad', 'Pear.good', 'Banana.bad', 'Potato.bad'} set2 = set() for s in set1: set2.add(s.removesuffix(".good").removesuffix(".bad")) 

Or create the new set using a set comprehension:

set2 = {s.removesuffix(".good").removesuffix(".bad") for s in set1} print(set2) 

Output:

{'Orange', 'Pear', 'Apple', 'Banana', 'Potato'} 

All you need is a bit of black magic!

>>> a = ["cherry.bad","pear.good", "apple.good"] >>> a = list(map(lambda x: x.replace('.good','').replace('.bad',''),a)) >>> a ['cherry', 'pear', 'apple'] 

When there are multiple substrings to remove, one simple and effective option is to use re.sub with a compiled pattern that involves joining all the substrings-to-remove using the regex OR (|) pipe.

import re to_remove = ['.good', '.bad'] strings = ['Apple.good','Orange.good','Pear.bad'] p = re.compile('|'.join(map(re.escape, to_remove))) # escape to handle metachars [p.sub('', s) for s in strings] # ['Apple', 'Orange', 'Pear'] 

You could do this:

import re import string set1={'Apple.good','Orange.good','Pear.bad','Pear.good','Banana.bad','Potato.bad'} for x in set1: x.replace('.good',' ') x.replace('.bad',' ') x = re.sub('\.good$', '', x) x = re.sub('\.bad$', '', x) print(x) 

# practices 2 str = "Amin Is A Good Programmer" new_set = str.replace('Good', '') print(new_set) print : Amin Is A Programmer 

I did the test (but it is not your example) and the data does not return them orderly or complete

>>> ind = ['p5','p1','p8','p4','p2','p8'] >>> newind = {x.replace('p','') for x in ind} >>> newind {'1', '2', '8', '5', '4'} 

I proved that this works:

>>> ind = ['p5','p1','p8','p4','p2','p8'] >>> newind = [x.replace('p','') for x in ind] >>> newind ['5', '1', '8', '4', '2', '8'] 

or

>>> newind = [] >>> ind = ['p5','p1','p8','p4','p2','p8'] >>> for x in ind: ... newind.append(x.replace('p','')) >>> newind ['5', '1', '8', '4', '2', '8'] 

If list

I was doing something for a list which is a set of strings and you want to remove all lines that have a certain substring you can do this

import re def RemoveInList(sub,LinSplitUnOr): indices = [i for i, x in enumerate(LinSplitUnOr) if re.search(sub, x)] A = [i for j, i in enumerate(LinSplitUnOr) if j not in indices] return A 

where sub is a patter that you do not wish to have in a list of lines LinSplitUnOr

for example

A=['Apple.good','Orange.good','Pear.bad','Pear.good','Banana.bad','Potato.bad'] sub = 'good' A=RemoveInList(sub,A) 

Then A will be