[issue41431] Optimize dict_merge for copy

[Inada Naoki]

New submission from Inada Naoki <songofacandy at gmail.com>:

Although there are dict.copy() and PyDict_Copy(), dict_merge can be used for copying dict.

* d={}; d.update(orig)
* d=dict(orig)
* d=orig.copy() # orig has many dummy keys.

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components: Interpreter Core
messages: 374550
nosy: inada.naoki
priority: normal
severity: normal
status: open
title: Optimize dict_merge for copy
versions: Python 3.10

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41431>
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