[issue21422] int << 0: return the number unmodified

[Mark Dickinson]

Mark Dickinson added the comment:

BTW, there's also a behaviour change here.  Before the patch:

>>> True << 0
1

After the patch:

>>> True << 0
True

Which demonstrates another good reason to avoid trivial-looking optimisations: it's far too easy to accidentally change behaviour.

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<http://bugs.python.org/issue21422>
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