Python 3 Map function is not Calling up function

Question

Why doesn't following code print anything:

#!/usr/bin/python3 class test:     def do_someting(self,value):         print(value)         return value      def fun1(self):         map(self.do_someting,range(10))  if __name__=="__main__":     t = test()     t.fun1() 

I'm executing the above code in Python 3. I think i'm missing something very basic but not able to figure it out.

Answer 1

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 deque  deque(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) 

Answer 2

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.