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importhook.cs breaks python's import interface #1245

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SStarosielec opened this issue Oct 5, 2020 · 2 comments
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importhook.cs breaks python's import interface #1245

SStarosielec opened this issue Oct 5, 2020 · 2 comments

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@SStarosielec
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SStarosielec commented Oct 5, 2020 •
edited by filmor
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Environment

  • Pythonnet version: 2.5.1
  • Python version: 3.7.9
  • Operating System: Windows 10

Details

  • Describe what you were trying to get done.

pythonnet overwrites the python's __import__ routine, but does not implement python's signature precisely:
original python's signature is

__import__(name, globals=None, locals=None, fromlist=(), level=0)

Most other python modules call the name parameter as positional: __import__("foo", ...

Some packages (e.g. kivy) use __import__ as

    __import__(
        name='{2}.{0}.{1}'.format(basemodule, modulename, base),
        globals=globals(), locals=locals(), fromlist=[modulename], level=0
    )

i.e. the name argument used as keyword argument in the call. Both calls are valid in python's __import__, but fail at the overwritten __import__ with

TypeError: __import__() takes at least 1 argument (0 given)

A hotfix is to alter the other modules code to

    __import__(
        '{2}.{0}.{1}'.format(basemodule, modulename, base),
        globals=globals(), locals=locals(), fromlist=[modulename], level=0
    )

but the broken code is within pythonnet.
@SStarosielec
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SStarosielec commented Oct 5, 2020 •
edited by filmor
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I'm not sure this section from https://docs.python.org/3/reference/expressions.html#calls applies (I don't understand all the lingo):

CPython implementation detail: An implementation may provide built-in functions whose positional parameters do not have names, even if they are ‘named’ for the purpose of documentation, and which therefore cannot be supplied by keyword. In CPython, this is the case for functions implemented in C that use PyArg_ParseTuple() to parse their arguments.

It then seems an incompatibiliy between python anc CPython, should CPython be fixed instead ?

@filmor
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filmor commented Oct 5, 2020

This should be relatively easy to fix and PRs are welcome, thank you for looking into this in detail (was reported before in #547).

The error here is partially on Kivy for calling __import__ directly instead of using importlib, and as you quoted we are kind-of allowed to make __import__ behave in this way.

Mid-term (hopefully in pythonnet 3), this should not be a problem anymore by implementing proper PEP302-style importing instead of overriding __import__.

This was referenced Jan 19, 2021
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@hiaselhans hiaselhans mentioned this issue May 5, 2021
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@filmor filmor closed this as completed Aug 8, 2021
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@filmor @SStarosielec