Python: casting map object to list makes map object empty?

Question

I have a map object that I want to print as a list but continue using as a map object afterwards. Actually I want to print the length so I cast to list but the issue also ha

Answer 1

The reason is that the Python 3 map returns an iterator and listing the elements of an iterator "consumes" it and there's no way to "reset" it

my_map = map(str,range(5))

list(my_map)
# Out: ['0', '1', '2', '3', '4']

list(my_map)
# Out: []

If you want to preserve the map object you can use itertools.tee to create a copy of the iterator to be used later

from itertools import tee

my_map, my_map_iter = tee(map(str,range(5)))

list(my_map)
# Out: ['0', '1', '2', '3', '4']

list(my_map)
# Out: []

list(my_map_iter)
# Out: ['0', '1', '2', '3', '4']