bpo-43977: Use tp_flags for collection matching #25723
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…tandard builtin classes.
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… Mapping to be special.
| @@ -499,6 +523,11 @@ _abc__abc_register_impl(PyObject *module, PyObject *self, PyObject *subclass) | |||
| /* Invalidate negative cache */ | |||
| get_abc_state(module)->abc_invalidation_counter++; | |||
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| if (PyType_Check(subclass) && PyType_Check(self) && | |||
| !PyType_HasFeature((PyTypeObject *)subclass, Py_TPFLAGS_IMMUTABLETYPE)) | |||
Modules/_abc.c
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| if (_PyDict_DelItemId(cls->tp_dict, &PyId___flags__) < 0) { | ||
| return NULL; | ||
| } |
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Why are we deleting __flags__ here? It looks like it will get overwritten anyways:
>>> class C:
... __flags__ = "Spam"
...
>>> C.__flags__
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The __flags__ set in Sequence is in Sequence.__dict__, but normally __flags__ is a descriptor.
So, it is probably safest to delete it. I suspect it doesn't matter much in practice.
Modules/_abc.c
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| @@ -446,6 +449,27 @@ _abc__abc_init(PyObject *module, PyObject *self) | |||
| return NULL; | |||
| } | |||
| Py_DECREF(data); | |||
| if (PyType_Check(self)) { | |||
| PyTypeObject *cls = (PyTypeObject *)self; | |||
| PyObject *flags = _PyDict_GetItemIdWithError(cls->tp_dict, &PyId___flags__); | |||
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Hm, this whole mechanism makes me a bit uncomfortable. I'm not aware of any case where writing to __flags__ in Pythonland actually works like this.
But I can't really think of anything better, so I guess it's fine. Maybe we could just use a name like _abc_tpflags or something instead of __flags__?
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Sure, it is just a name. I like using a dunder name, as it is a special thing. __abc_tpflags__ perhaps?
| Use tp_flags on the class object to determine if the subject is a sequence | ||
| or mapping when pattern matching. Avoids the need to import collections.abc | ||
| when pattern matching. |
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Just some markup to make this a bit richer:
| Use tp_flags on the class object to determine if the subject is a sequence | |
| or mapping when pattern matching. Avoids the need to import collections.abc | |
| when pattern matching. | |
| Use :c:member:`~PyTypeObject.tp_flags` on the class object to determine if the subject is a sequence | |
| or mapping when pattern matching. Avoids the need to import :mod:`collections.abc` | |
| when pattern matching. |
Lib/_collections_abc.py
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| @@ -793,6 +793,7 @@ def __isub__(self, it): | |||
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| ### MAPPINGS ### | |||
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| TPFLAGS_MAPPING = 1 << 6 | |||
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If this is public and can be relied upon, it needs to be added to the docs for collections.abc
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This should be internal. I'll hide it.
Py_TPFLAGS_SEQUENCEandPy_TPFLAGS_MAPPINGMATCH_SEQUENCEandMATCH_MAPPINGto avoid importingcollections.abcwhen matching.https://bugs.python.org/issue43977