[pypy-issue] Issue #2885: Document pypy3's use of keyed hash function. (pypy/pypy)

[Ryan Hileman]

New issue 2885: Document pypy3's use of keyed hash function.
https://bitbucket.org/pypy/pypy/issues/2885/document-pypy3s-use-of-keyed-hash-function

Ryan Hileman:

The docs claim PyPy ignores hash randomization:

http://doc.pypy.org/en/latest/cpython_differences.html#miscellaneous

> Hash randomization (-R) is ignored in PyPy. In CPython before 3.4 it has little point.

However, after asking on IRC, it appears pypy3 *does* use SipHash by default (presumably with a randomized key), but still ignores the -R flag (which doesn't matter because it's on by default).

mjacob from IRC:
> we didn't follow CPython in implementing their first (unsuccessful) attempt to fix the problem
> however we followed CPython in implementing the second attempt to fix the problem with a cryptographic hash function
> (see also sys.hash_info)

I think the cpython_differences doc should be updated to say this is not an issue in pypy3 (if this information is correct).