[issue17566] Make importlib.abc.Loader.module_repr optional

[Brett Cannon]

Changes by Brett Cannon <brett at python.org>:


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components: +Library (Lib) -Documentation
title: Document that importlib.abc.Loader.module_repr is abstract and thus needed by various other ABCs -> Make importlib.abc.Loader.module_repr optional
versions:  -Python 3.3

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue17566>
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