support IPython DummyMod as __main__ module for pytest fixtures #12965
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nicoddemus
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Thanks @smacke for the PR.
I'm hesitant to add this hack to the collection code.
Wouldn't make more sense for IPython to change DummyMod to subclass from types.ModuleType? This would not need changes in pytest, while it would also be compatible with anything else that might inspect the module.
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Yeah, agree fixing in IPython makes more sense. |
Carreau
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… user_ns (#14754) ## What changes are proposed in this pull request? Some IPython apps, such as the one used in Databricks, need to seed the shell with a custom user namespace before it is actually created. This means the main module used by ipython can’t be a normal ModuleType (which doesn’t support overwriting __dict__) but instead a custom “DummyMod”. DummyMod isn’t considered an instance of ModuleType, which can mess up tools like ipytest + pytest -- see, for example, pytest-dev/pytest#12965. To fix, in this PR we create a helper function that generates a `ModuleType` subclass on-the-fly and that uses the user namespace provided a priori as its `__dict__`. Note that `ModuleType.__dict__` is read-only, which is probably why IPython originally created DummyMod. To get around that, we create a `__dict__` property and use custom getters / setters to delegate to the user_ns we pass in. Searching around, it seems like `DummyMod` / `FakeModule` may have caused some pain points in the past, e.g. around pickling (#384, #112) -- still trying to determine if this change can help with that. ## How is this tested? Manual + pre-merge
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This PR fixes a corner case when using ipytest with certain IPython environments. Some environments, such as Databricks, use an IPython feature where the user_ns of the interactive shell is specified ahead of time. Because this user_ns doubles as the main module's
__dict__, the official module type cannot be used, since__dict__is a read-only attribute. To work around this, IPython uses a fake module type calledDummyModto handle this case. However, instances ofDummyModdo not pass the isinstance check added in c6a5290. To fix, check if we've imported the module that containsDummyMod, and if so, addDummyModto the isinstance check.Test plan: verified manually.