python: calling set over Itertools product object second time clear data

Question

when calling set(c) second time it show empty set, it clear data butit working fine for first time and address of object is also same .

>>> import itertools
>>> a = ["aaa", "bbb", "ccc"]
>>> b = [True, False]
>>> c = itertools.product(a, b)
>>> c
<itertools.product object at 0x7f7bbca23050>
>>> set(c)
set([('bbb', True), ('ccc', True), ('ccc', False), ('aaa', True), ('bbb', False), ('aaa', False)])
>>> set(c)
set([])
>>> c
<itertools.product object at 0x7f7bbca23050>

Answer 1

you exhaust the generator c the first time you call set.

other example:

import itertools
a = ["aaa", "bbb", "ccc"]
b = [True, False]
c = itertools.product(a, b)

for item in c:
    print(item) 
for item in c:
    print(item)

the second loop will not print anything.

if you need to be able to iterate twice over the same iterator, you can use itertools.tee:

from itertools import tee

c1, c2 = tee(c)

now you have 2 independent iterators.