Are there any list comparison optimizations in Python?

Peter Hansen peter at
Tue Nov 13 03:40:59 CET 2001

"Jonathan P." wrote:
> One of Python's most convenient high-level features is automatic list
> comparison by value and recursively.
> Does it know to optimize the compare if it has already been determined
> that two items share a reference to the same object by not doing a
> value compare on them anymore?

I just created two million-integer lists with "[0] * 1000000" and 
compared them, then reassigned the second name to reference the
first list and compared again.  There was a noticeable pause during
both compares (with "==").

Comparing two lists with different lengths *does* return

Peter Hansen, P.Eng.
peter at

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