Why doesn't .strip() remove whitespaces?

Question

I have a function that begins like this:

def solve_eq(string1):
    string1.strip(' ')
    return string1

I'm inputting the string '1 + 2 * 3 ** 4' but the return statement is not stripping the spaces at all and I can't figure out why. I've even tried .replace() with no luck.

Strings are immutable so don't expect anything to act on them in-place. Use the return value of `string1.strip()`. — Andras Deak -- Слава Україні, Nov 06 '16 at 00:29
I need to further modify the string, so could I do something like string2 = string1.strip (' ') ? — Lanier Freeman, Nov 06 '16 at 00:31
Try it. (That was exactly my point). You can also rebind `string1 = string1.strip(' ')`. — Andras Deak -- Слава Україні, Nov 06 '16 at 00:31
strip will not do what you want. strip removes *trailing* and *leading* whitespace. This is simply a matter of string immutability and using `string1.replace(' ', '')` to solve this problem. — idjaw, Nov 06 '16 at 00:34
Jeez, so much downvoting here... if you strip '1 + 2 * 3 ** 4', you get '1 + 2 * 3 ** 4'. Not really fair to downvote... — Eugene, Nov 06 '16 at 00:37
What exactly do you want this function to return? `"1+2*3**4"`? `163`? — Jordan McQueen, Nov 06 '16 at 00:37
@JordanMcQueen The function has to recursively evaluate an equation that is a string parameter. I have to account for spaces in the parameter initially. — Lanier Freeman, Nov 06 '16 at 00:40
Does this answer your question? [Why doesn't calling a Python string method do anything unless you assign its output?](https://stackoverflow.com/questions/9189172/why-doesnt-calling-a-python-string-method-do-anything-unless-you-assign-its-out) — Georgy, May 11 '20 at 18:58

score 22 · Accepted Answer · edited Oct 27 '21 at 19:47

22

strip does not remove whitespace everywhere, only at the beginning and end. Try this:

def solve_eq(string1):
    return string1.replace(' ', '')

This can also be achieved using regex:

import re

a_string = re.sub(' +', '', a_string)

edited Oct 27 '21 at 19:47

Tomerikoo

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answered Nov 06 '16 at 00:34

Eugene

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I'm one of the downvoters. Don't take this personally, and most certainly don't give up on SO. The reason I downvoted the answer is that OP has a very fundamental misconception of how strings and related methods work. The main issue is not using the return value of `.strip()`, but rather thinking that the method mutates the input string. Questions like this pop up like mushrooms, and are essentially typo questions (not actual typos, but brain farts). Answering such questions will stop automatic deletion processes to kick in once the question is closed. You're wasting your time answering them. – Andras Deak -- Слава Україні Nov 06 '16 at 00:51
2

I'm a robot, I never take things personally... Yeah, "I've even tried `.replace()`" kinda gives it away. But downvoting as opposed to a request to delete in the comments? I'm only in it for the points ;) You're totally right though, questions need to be filtered, or at least immediately tagged based on points or something. The large majority of the questions I answer, I do so using SO! Maybe SO should make available a JFGI flag for noobs? Ha! Anyway, thanks for the explanation, appreciate it. – Eugene Nov 06 '16 at 01:02

score 9 · Answer 2 · edited Oct 27 '21 at 19:51

9

strip doesn't change the original string since strings are immutable. Also, instead of string1.strip(' '), use string1.replace(' ', '') and set a return value to the new string or just return it.

Option 1:

def solve_eq(string1):
    string1 = string1.replace(' ', '')
    return string1

Option 2:

def solve_eq(string1):
    return string1.replace(' ', '')

edited Oct 27 '21 at 19:51

Tomerikoo

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answered Nov 06 '16 at 00:34

Marissa Novak

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score 2 · Answer 3 · answered Nov 06 '16 at 00:30

2

strip returns the stripped string; it does not modify the original string.

answered Nov 06 '16 at 00:30

Scott Hunter

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I suspected this had something to do it. Any reason why Python works this way out of curiosity? – Lanier Freeman Nov 06 '16 at 00:32
4

@Lanier How about my comment that explains this? – Andras Deak -- Слава Україні Nov 06 '16 at 00:33

Why doesn't .strip() remove whitespaces?

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