[New-bugs-announce] [issue29403] mock's autospec's behavior on method-bound builtin functions is broken

[Aaron Gallagher]

New submission from Aaron Gallagher:

Cython will, in the right circumstances, offer a MethodType instance where im_func is a builtin function. Any instance of MethodType is automatically assumed to be a python-defined function (more specifically, a function that has an inspectable signature), but _set_signature was still conservative in its assumptions. As a result _set_signature would return early with None instead of a mock since the im_func had no inspectable signature. This causes problems deeper inside mock, as _set_signature is assumed to always return a mock, and nothing checked its return value.

In similar corner cases, autospec will simply not check the spec of the function, so _set_signature is amended to now return early with the original, not-wrapped mock object.

There is another None early return in _set_signature, but it seems.. harder to trigger? It seems more appropriate to raise an exception there if this is being fixed.

----------
components: Library (Lib)
messages: 286565
nosy: Aaron Gallagher
priority: normal
severity: normal
status: open
title: mock's autospec's behavior on method-bound builtin functions is broken
type: behavior
versions: Python 2.7, Python 3.3, Python 3.4, Python 3.5, Python 3.6, Python 3.7

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue29403>
_______________________________________