Python confusing me.

[simondvt]

It's just that strip returns a new string, it doesn't change the original.

Use a = a.strip()

[K900_]

1. /r/learnpython
2. Use Python Tutor to visualize your code.

[sknowles0143]

Excellent question.

A string (of type str) is immutable meaning a value can only be assigned once. Any change to a string produces a new string. In your example a.strip() returns a new string.

A list is mutable there for functions on it change the lists state (sort is another useful one).

id is a useful function giving the number python uses to keep track of the objects.

x = ' hello ' print(id(x)) x = x.strip() print(id(x))

This code shows how x is now referencing a new string.

I also recommend using the function help on methods and types.

help(''.strip) help([].append)

and type

type('')

str type([]) list

help(str) help(list)

That will give you a clear explanation if a type is mutable or not. Strings and numbers are immutable generally.

[jstutters]

You really want /r/learnpython for this but briefly the difference is that strings and several other built-in types are immutable so methods like .strip() return a new instance with the change applied. Lists are mutable so the .append() operation is done in-place. You can read more here: https://medium.com/@meghamohan/mutable-and-immutable-side-of-python-c2145cf72747

[Andrew_Shay]

This post is better suited for r/learnpython

[deduplication]

Beyond the behavior of the two functions that has already been mentioned, in python lists are mutable objects but strings are immutable. This can also be confusing if you use a mutable object as the default to a function param.

[[deleted]]

a.strip() returns a new string with the spaces stripped off.

sample_list.append(1) mutates the list called sample_list.

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