Why does `is` return False even though id's are identical?

Damian Published at Dev

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damian

I already looked at this question, but I don't really get why the two id() calls return an identical value, while the is comparison returns False.

>>> [2,2,2] + [1] == [2,2,2,1]
True
>>> [2,2,2] + [1] is [2,2,2,1]
False
>>> id([2,2,2] + [1])
4396847688
>>> id([2,2,2,1])
4396847688

To be sure, I did expect the two comparisons to return True and False as they did, I just don't get why the ids are not different.

Tim Peters

Just re-entering my comment as "an answer":

Simply because the same memory is reused for the objects: in the last two statements, the lifetimes of the objects whose id's you're obtaining do not overlap, so Python is free to (re)use the same memory for them.

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edited at2020-10-26

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