cycle(p) --> p0, p1, ... plast, p0, p1, …
Return elements from the iterable p until it is exhausted. Then repeat the sequence indefinitely.
>>> from itertools import cycle
>>> x = cycle("abcd")
>>> for _ in range(10):
... print(next(x), end=", ")
...
a, b, c, d, a, b, c, d, a, b,