Python map function strange behavior

Question

I´m running the following code:

selectedvalidations='1,2,3,4,5,6,7'
x=map(int,selectedvalidations.split(','))
print(list(x))

It prints:

[1, 2, 3, 4, 5, 6, 7]

If I print again:

print(list(x))

It prints:

[]

Why?

because map is generator, you extract all from this generator and it is empty, try `new_x = list(x)` and `print(new_x)` how many times you want — Druta Ruslan, May 29 '18 at 12:19
The clearest thing to do in this case is to avoid map and use a list comprehension. — Paul Rooney, May 29 '18 at 12:32

Rakesh · Answer 1 · 2018-05-29T12:22:04.543

1

In python3 map is a generator. If you want to reuse the variable use

selectedvalidations='1,2,3,4,5,6,7'
x=list(map(int,selectedvalidations.split(',')))  #Encapsulate map in list
print(x)

edited May 29 '18 at 12:22

answered May 29 '18 at 12:20

Rakesh

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why you use two times `list()` ? – Druta Ruslan May 29 '18 at 12:21
Sorry did not see that. Thanks – Rakesh May 29 '18 at 12:21
Tks! In Python 2.7 the behavior is different, that is, I can use "x" map object many times without problem. – Mauro Assis May 29 '18 at 13:18
You are right in python2 map returns a list so you can use any number of times. – Rakesh May 29 '18 at 13:20

score 0 · Answer 2 · answered May 29 '18 at 12:22

The right way to do it is to convert the generator into list in-place and hold the list in the variable

>>> selectedvalidations='1,2,3,4,5,6,7'
>>> x=list(map(int,selectedvalidations.split(',')))
>>> x
[1, 2, 3, 4, 5, 6, 7]
>>> x
[1, 2, 3, 4, 5, 6, 7]
>>>

Python map function strange behavior

2 Answers2