Python 3.x returns a generator object:
$ python3 -c "print(map(lambda x: 2**x, range(7)))"
You can extract those values using list(), but generators can be depleted. Hence subsequent use of list() will result in an empty [] since there are no more values to access with next() calls. I'd recommend experimenting with generators a little, or read a bit here https://wiki.python.org/moin/Generators. Hope this helps
