python - Why does hash(None) change across different platforms and in different calls? -


i'm facing weird behavior hash function on python. when run following command on mac os (10.10) different values different calls.

$ python -c "print hash(none)" -9223372036579216774 $ python -c "print hash(none)" -9223372036582852230

in other hand when run same thing on ubuntu 14.04 get:

$ python -c "print hash(none)" 596615 $ python -c "print hash(none)" 596615

for me looks like, in os x, python using memory address somehow , ubuntu not. can see hash function implementation dependent. shouldn't based on "value" of none only? numbers represent? why behave differently on same python version on different os?

none.__hash__ correlates _py_hashpointer hashing function. pointer of object used hash. none beeing singleton safe use, not deterministic. pointer cast adequate integer type p hash value calculated following:

    (p >> 4) | (p << (8 * sizeof_void_p - 4))

referring comment in source code states:

bottom 3 or 4 bits 0; rotate y 4 avoid excessive hash collisions dicts , sets


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