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gh-77753: Add example for values that compare equal in stdtypes #98497

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Merged
JelleZijlstra merged 3 commits into from
Oct 26, 2022
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gh-77753: Add example for values that compare equal in stdtypes #98497

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8a0b80c
Add example for values that compare equal in stdtypes
slateny Jul 20, 2022
b95d14d
Rephrase succinctly
slateny Oct 21, 2022
f992fd5
Remove floating-point note
slateny Oct 21, 2022
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8 changes: 3 additions & 5 deletions Doc/library/stdtypes.rst
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Expand Up @@ -4370,11 +4370,9 @@ type, the :dfn:`dictionary`. (For other containers see the built-in
A dictionary's keys are *almost* arbitrary values. Values that are not
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@JelleZijlstra JelleZijlstra Oct 20, 2022

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I don't like this "almost arbitrary values" wording, since several very common types (lists, dicts, sets) can't be used as dict keys. No need to change that in this PR though.

:term:`hashable`, that is, values containing lists, dictionaries or other
mutable types (that are compared by value rather than by object identity) may
not be used as keys. Numeric types used for keys obey the normal rules for
numeric comparison: if two numbers compare equal (such as ``1`` and ``1.0``)
then they can be used interchangeably to index the same dictionary entry. (Note
however, that since computers store floating-point numbers as approximations it
is usually unwise to use them as dictionary keys.)
not be used as keys.
Values that compare equal (such as ``1``, ``1.0``, and ``True``)
can be used interchangeably to index the same dictionary entry.

.. class:: dict(**kwargs)
dict(mapping, **kwargs)
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