Python 3 Map function is not Calling up function
map()
returns an iterator, and will not process elements until you ask it to.
Turn it into a list to force all elements to be processed:
list(map(self.do_someting,range(10)))
or use collections.deque()
with the length set to 0 to not produce a list if you don't need the map output:
from collections import dequedeque(map(self.do_someting, range(10)))
but note that simply using a for
loop is far more readable for any future maintainers of your code:
for i in range(10): self.do_someting(i)
Before Python 3, map() returned a list, not an iterator. So your example would work in Python 2.7.
list() creates a new list by iterating over its argument. ( list() is NOT JUST a type conversion from say tuple to list. So list(list((1,2))) returns [1,2]. ) So list(map(...)) is backwards compatible with Python 2.7.
I just want to add the following:
With multiple iterables, the iterator stops when the shortest iterable is exhausted
[ https://docs.python.org/3.4/library/functions.html#map ]
Python 2.7.6 (default, Mar 22 2014, 22:59:56)
>>> list(map(lambda a, b: [a, b], [1, 2, 3], ['a', 'b']))[[1, 'a'], [2, 'b'], [3, None]]
Python 3.4.0 (default, Apr 11 2014, 13:05:11)
>>> list(map(lambda a, b: [a, b], [1, 2, 3], ['a', 'b']))[[1, 'a'], [2, 'b']]
That difference makes the answer about simple wrapping with list(...)
not completely correct
The same could be achieved with:
>>> import itertools>>> [[a, b] for a, b in itertools.zip_longest([1, 2, 3], ['a', 'b'])][[1, 'a'], [2, 'b'], [3, None]]