how to use strip in map function

Question

I'd like to use map to get list of strings:

value = '1, 2, 3'

my_list = list(map(strip, value.split(',')))

but got:

NameError: name 'strip' is not defined

expected result: my_list=['1','2','3']

`map()` doesn't return a list. Do you mean `list(map(...))` perhaps? — Martijn Pieters, Oct 05 '16 at 13:44
related: http://stackoverflow.com/questions/12182777/is-there-a-better-way-to-use-strip-on-a-list-of-strings-python — Dimitris Fasarakis Hilliard, Oct 05 '16 at 13:49
This is not a duplicate question, even if the underlying problem is the same: this question asks specifically about `map`, while the other question does not, and the accepted answer there uses list comprehension instead of `map`, an arguably inferior solution to the problem. — MestreLion, Jul 28 '20 at 13:39
At best, this could be a duplicate of the question @DimitrisFasarakisHilliard mentioned as related — MestreLion, Jul 28 '20 at 13:41

score 44 · Accepted Answer · answered Oct 05 '16 at 13:42

44

strip is still just a variable, not a reference to the str.strip() method on each of those strings.

You can use the unbound str.strip method here:

my_list = list(map(str.strip, value.split(',')))

which will work for any str instance:

>>> value = '1, 2, 3'
>>> list(map(str.strip, value.split(',')))
['1', '2', '3']

In case you want to call a method named in a string, and you have a variety of types that all happen to support that method (so the unbound method reference wouldn't work), you can use a operator.methodcaller() object:

from operator import methodcaller

map(methodcaller('strip'), some_mixed_list)

However, instead of map(), I'd just use a list comprehension if you want to output a list object anyway:

[v.strip() for v in value.split(',')]

answered Oct 05 '16 at 13:42

Martijn Pieters

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Perfect answer, first I use map to convert '1, 2, 3' into [1,2,3] list(map(int,value)), but than I changed mind and fixed on map. But list comprehension is more pythonish – Tomasz Brzezina Oct 06 '16 at 08:41
@TomaszBrzezina: I think the `map` approach is as pythonic as the list comprehension. `map` is *meant* for this use case. It's also shorter and performs better as a bonus. – MestreLion Jul 28 '20 at 13:33
What if we want to strip something other than space? Like `_` How do we pass it ? – Hayat Dec 14 '20 at 02:46
@Hayat `methodcaller()` also takes arguments: `methodcaller('strip', '_')` – Martijn Pieters Dec 15 '20 at 08:59

score 7 · Answer 2 · edited Oct 05 '16 at 14:39

7

You can also use a lambda to achieve your purpose by using:

my_list = map(lambda x:x.strip(), value.split(","))

where each element in value.split(",") is passed to lambda x:x.strip() as parameter x and then the strip() method is invoked on it.

edited Oct 05 '16 at 14:39

Dimitris Fasarakis Hilliard

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answered Oct 05 '16 at 13:59

Zixian Cai

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how to use strip in map function

2 Answers2