[issue25532] infinite loop when running inspect.unwrap over unittest.mock.call

[Nick Coghlan]

Nick Coghlan added the comment:

An alternative approach would be to change inspect.unwrap() to use getattr_static() rather than the usual getattr().

The downside of that would be potentially breaking true object proxies, like the 3rd party wrapt module and weakref.proxy.

However, what if inspect.signature implemented a limit on the number of recursive descents it permitted (e.g. based on sys.getrecursionlimit()), and then halted the descent, the same way it does if it finds a `__signature__` attribute on a wrapped object?

`inspect.unwraps` makes that relatively straightforward:

    unwrap_count = 0
    recursion_limit = sys.getrecursionlimit()
    def stop_unwrapping(wrapped):
        nonlocal unwrap_count
        unwrap_count += 1
        return unwrap_count >= recursion_limit
    innermost_function = inspect.unwrap(outer_function, stop=stop_unwrapping)

Alternatively, that hard limit on the recursive descent could be baked directly into the loop detection logic in inspect.unwrap (raising ValueError rather than returning the innermost function reached), as Chris suggested above. We'd then just need to check inspect.signature was handling that potential failure mode correctly.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue25532>
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