STINNER Victor <[email protected]> added the comment:
> Code extremely simplified: (...)
Relationship between origin unmodified code and the extremely simplified code:
* Lib/test/test_importlib/__init__.py: load_tests() is called at each "test -R
3:3" iteration
* Lib/test/test_importlib/test_windows.py: at each iteartion:
* machinery =
test.test_importlib.util.import_importlib('importlib.machinery') is called: it
reloads the whole importlib package, with _frozen_importlib and
_frozen_importlib_external blocked (force to reload pure Python
importlib._bootstrap and importlib._bootstrap_external modules)
* support.import_module('winreg', required_on=['win']) is called with the
fresh new importlib package: in short, it tries to import winreg which fails
with ModuleNotFoundError
* Lib/importlib/__init__.py: each time the module is reloaded
* importlib._bootstrap._setup() is called: it copies '_thread', '_warnings'
and '_weakref' from sys.modules into importlib._bootstrap namespace (module
globals) using setattr(self_module, ...)
* importlib._bootstrap_external._setup() is called: it calls
_bootstrap._builtin_from_name('_weakref')
When importlib._bootstrap_external._setup() calls
_bootstrap._builtin_from_name('_weakref'), _init_module_attrs() copies the
"spec" into module.__spec__. But the spec contains a reference to
importlib._bootstrap namespace.
Before _weakref is converted to multiphase initialization:
$ ./python
>>> import _weakref
>>> id(_weakref)
140119879580176
>>> id(_weakref.__spec__.__init__.__globals__['_weakref'])
140119879580176
=> same module
After the change:
$ ./python
>>> import _weakref
>>> id(_weakref)
140312826159952
>>> id(_weakref.__spec__.__init__.__globals__['_weakref'])
140312826366288
=> two different objects
The problem is that module.__spec__ pulls the whole importlib package which
contains tons of objects.
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Python tracker <[email protected]>
<https://bugs.python.org/issue40050>
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