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45 lines
1.6 KiB
ReStructuredText
45 lines
1.6 KiB
ReStructuredText
7 years ago
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Module Import Wall Of Shame
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---------------------------
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The following modules and packages run magic during ``__init.py__`` that makes
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life hard for Mitogen. Executing code during module import is always bad, and
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Mitogen is a concrete benchmark for why it's bad.
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``pkg_resources``
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=================
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Anything that imports ``pkg_resources`` will eventually cause
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pkg_resources to try and import and scan ``__main__`` for its ``__requires__``
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attribute (``pkg_resources/__init__.py::_build_master()``). This breaks any app
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that is not expecting its ``__main__`` to suddenly be sucked over a network and
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injected into a remote process, like py.test.
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A future version of Mitogen might have a more general hack that doesn't import
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the master's ``__main__`` as ``__main__`` in the slave, avoiding all kinds of
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issues like these.
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**What could it do instead?**
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* Explicit is better than implicit: wait until the magical behaviour is
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explicitly requested (i.e. an API call).
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* Use ``get("__main__")`` on :py:attr:`sys.modules` rather than ``import``, but
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this method isn't general enough, it only really helps tools like Mitogen.
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``pbr``
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=======
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It claims to use ``pkg_resources`` to read version information
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(``_get_version_from_pkg_metadata()``), which would result in PEP-302 being
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reused and everything just working wonderfully, but instead it actually does
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direct filesystem access. So we smodge the environment with a ``PBR_VERSION``
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environment variable to override any version that was defined. This will
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probably break code I haven't seen yet.
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**What could it do instead?**
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* ``pkg_resources.get_resource_stream()``
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