Python: How to str.replace multiple different strings with the same replacement?

Question

I am trying to replace multiple different strings with the same string replace rule.

list_names = ['!sdf?', '!sdfds?', '!afsafsa?', '!afasf?']

for i in list_names:
    vari1 = list_names[1]
    vari2 = list_names[2]
    vari3 = list_names[3]

I am trying to replace the ! and the ? above with ''.

At the moment I can do this string by string using the below code:

list_names = ['!sdf?', '!sdfds?', '!afsafsa?', '!afasf?']
for i in list_names:
    vari1 = list_names[1]
    vari2 = list_names[2]
    vari3 = list_names[3]
    vari1 = vari1.replace('!', '').replace('?', '')
    vari2 = vari2.replace('!', '').replace('?', '')
    vari3 = vari3.replace('!', '').replace('?', '')

I am aware it doesn't make sense to use a loop in the above code. But I intend to build on this.

Given that the string replaces are the same for all 3 variables, is there any easy way to do this for all of them at once?

Thanks!

ThePyGuy · Accepted Answer · 2021-07-04 11:52:00Z

6

You can just use List-comprehension.

>>> [x.replace('!', '').replace('?','') for x in list_names]
['sdf', 'sdfds', 'afsafsa', 'afasf']

Also, if you have multiple strings to replace, you can even use regular expression combining them by | using re.sub function as mentioned below:

>>> import re
>>> [re.sub('\?|!', '', x) for x in list_names]
['sdf', 'sdfds', 'afsafsa', 'afasf']

edited Jul 4, 2021 at 11:52

answered Jul 4, 2021 at 11:45

ThePyGuy

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1 Comment

user14887424 Over a year ago

It is good but here it is for others to note about re method: It can be very slow on large data and thus using regex only for small database is suggested.

user14887424 · Accepted Answer · 2021-07-04 11:45:16Z

2

You are doing wrong code. You can simply iterate through the indices of the list and convert all of them just like below:

list_names = ['!sdf?', '!sdfds?', '!afsafsa?', '!afasf?']
for index in range(len(list_names)):
    list_names[index] = list_name[index].replace("!", '').replace('?', '')

how does `range(len(list_names))` work?

first the length of list_names is calculated which in this case is 4. Now using range function we are able to get a list [0, 1, 2, 3] which are all the possible indices. By going through the list replacing each index we are able to update values.

answered Jul 4, 2021 at 11:45

user14887424

Comments

fsimonjetz · Accepted Answer · 2021-07-04 11:53:46Z

2

If the characters to replace are only at the start or end of the string just use strip('!?'):

for n in list_names:
    print(n.strip('!?'))

If you need to replace something anywhere in the string, you need a regular expression as others suggested:

import re

for n in list_names:
    print(re.sub('[?!]', '', n))

edited Jul 4, 2021 at 11:53

answered Jul 4, 2021 at 11:47

fsimonjetz

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iampritamraj · Accepted Answer · 2021-07-04 12:10:36Z

1

This also works if you want in single line without list comprehension

import ast

list_names = ['!sdf?', '!sdfds?', '!afsafsa?', '!afasf?']

modified_list_names = ast.literal_eval(str(list_names).replace("!",".").replace("?","."))

print(modified_list_names)

answered Jul 4, 2021 at 12:10

iampritamraj

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Stepan Dyatkovskiy · Accepted Answer · 2021-07-04 13:03:07Z

Consider using maps:

list_names = ['!sdf?', '!sdfds?', '!afsafsa?', '!afasf?']
list_names = [*map(lambda s: s.replace(...), list_names)]

If you just need a collection, and want to enumerate it once, then more efficient not to convert it to list, so it would be:

list_names = ['!sdf?', '!sdfds?', '!afsafsa?', '!afasf?']
list_names_map = map(lambda s: s.replace(...), list_names)

Actual execution of map will be postponed till place where you put it into for clause.

It might be also helpfull if you want the result to be changed whenever you change source collection. Special case is DB query of big amount of records, which might be done within series embedded queries.

As it was noticed by @ThePyGuy, another step to improve performance is to use single pass replacement for two symbols, depending on interpreter type, it might re.sub or a direct implementation:

import re
list_names = ['!sdf?', '!sdfds?', '!afsafsa?', '!afasf?']
list_names_map = map(lambda s: re.sub(r'[\?\!]', '', s), list_names)

# Do you still need a list?
list_names = list(list_names_map)

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how does `range(len(list_names))` work?