CODEWITHSUNDEEP
pythonpython-itertoolsteepython-zip
John Sekar
John Sekar

Reputation: 1

Can someone explain this interaction between `zip` and `tee` from itertools?

From my understanding, tee is supposed to make independent copies of an iterator, each of which can be exhausted individually. However, when exhausting the teed copies, sometimes the original iterator is intact, and at other times (e.g., when zip is involved), it is exhausted instead. Why is this happening? Am I missing some nuance in the semantics of tee and zip?

Expected behavior for range(3). The original iterator is intact and can be exhausted separately.

a = range(3)
a1,a2 = tee(a,2)
print(list(a1), list(a2), list(a))
>> [0, 1, 2], [0, 1, 2], [0, 1, 2]

Unexpected behavior for zip(range(3),range(3,6)). The original iterator is exhausted when the copies are exhausted.

a = zip(range(3),range(3,6))
a1,a2 = tee(a,2)
print(list(a1), list(a2), list(a))
>> [(0, 3), (1,4), (2,5) ], [(0, 3), (1, 4), (2,5)], []

Upvotes: -1

Views: 55

Answers (1)

John Sekar
John Sekar

Reputation: 1

Following comment by Michael Butcher, range(3) is an iterable, whereas iter(range(3)) is an iterator, which behaves similar to zip(...).

a = iter(range(3))
a1,a2 = tee(a,2)
print(list(a1),list(a2),list(a)
>> [0, 1, 2], [0, 1, 2], []

Upvotes: 0

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