[issue12542] Remove duplicates of cmp_to_key used in tests

[Éric Araujo]

Changes by Éric Araujo <merwok at netwok.org>:


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resolution: accepted -> fixed
stage: commit review -> committed/rejected
status: open -> closed

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue12542>
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