[issue20422] Signature.from_builtin should raise a ValueError when no signature can be provided

[Yury Selivanov]

New submission from Yury Selivanov:

Right now it may return `None` if no signature can be returned for the given builtin. If we decide to implement #17373 in 3.5, I'd like all three methods -- from_builtin, from_function, from_callable -- to either return a signature or to raise an exception.

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messages: 209565
nosy: brett.cannon, larry, ncoghlan, yselivanov
priority: normal
severity: normal
status: open
title: Signature.from_builtin should raise a ValueError when no signature can be provided
type: behavior
versions: Python 3.4

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue20422>
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