[New-bugs-announce] [issue19224] Make hash(None) consistent among processes

[Qiangning Hong]

New submission from Qiangning Hong:

Integers, strings, and bool's hash are all consistent for processes of a same interpreter.  However, hash(None) differs.

$ python -c "print(hash(None))"
272931276
$ python -c "print(hash(None))"
277161420

It's wired and make difficulty for distributed systems partitioning data according hash of keys if the system wants the keys support None.

This patch makes hash(None) always return 0 to resolve that problem.  And it is used in DPark(Python clone of Spark, a MapReduce alike framework in Python, https://github.com/douban/dpark) to speed up portable hash (see line https://github.com/douban/dpark/blob/65a3ba857f11285667c61e2e134dacda44c13a2c/dpark/util.py#L47).

davies.liu at gmail.com is the original author of this patch.  All credit goes to him.

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messages: 199439
nosy: hongqn
priority: normal
severity: normal
status: open
title: Make hash(None) consistent among processes

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue19224>
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