[Python-checkins] bpo-36743: __get__ is sometimes called without the owner argument (#12992)
Raymond Hettinger
webhook-mailer at python.org
Thu Aug 29 04:27:46 EDT 2019
https://github.com/python/cpython/commit/0dac68f1e593c11612ed54af9edb865d398f3b05
commit: 0dac68f1e593c11612ed54af9edb865d398f3b05
branch: master
author: Raymond Hettinger <rhettinger at users.noreply.github.com>
committer: GitHub <noreply at github.com>
date: 2019-08-29T01:27:42-07:00
summary:
bpo-36743: __get__ is sometimes called without the owner argument (#12992)
files:
M Doc/reference/datamodel.rst
M Lib/_pyio.py
M Lib/functools.py
M Lib/unittest/mock.py
M Tools/demo/eiffel.py
diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst
index d1702ccb6417..8813f57587f0 100644
--- a/Doc/reference/datamodel.rst
+++ b/Doc/reference/datamodel.rst
@@ -1618,21 +1618,32 @@ refers to the attribute whose name is the key of the property in the owner
class' :attr:`~object.__dict__`.
-.. method:: object.__get__(self, instance, owner)
+.. method:: object.__get__(self, instance, owner=None)
- Called to get the attribute of the owner class (class attribute access) or of an
- instance of that class (instance attribute access). *owner* is always the owner
- class, while *instance* is the instance that the attribute was accessed through,
- or ``None`` when the attribute is accessed through the *owner*. This method
- should return the (computed) attribute value or raise an :exc:`AttributeError`
- exception.
+ Called to get the attribute of the owner class (class attribute access) or
+ of an instance of that class (instance attribute access). The optional
+ *owner* argument is the owner class, while *instance* is the instance that
+ the attribute was accessed through, or ``None`` when the attribute is
+ accessed through the *owner*.
+ This method should return the computed attribute value or raise an
+ :exc:`AttributeError` exception.
+
+ :PEP:`252` specifies that :meth:`__get__` is callable with one or two
+ arguments. Python's own built-in descriptors support this specification;
+ however, it is likely that some third-party tools have descriptors
+ that require both arguments. Python's own :meth:`__getattribute__`
+ implementation always passes in both arguments whether they are required
+ or not.
.. method:: object.__set__(self, instance, value)
Called to set the attribute on an instance *instance* of the owner class to a
new value, *value*.
+ Note, adding :meth:`__set__` or :meth:`__delete__` changes the kind of
+ descriptor to a "data descriptor". See :ref:`descriptor-invocation` for
+ more details.
.. method:: object.__delete__(self, instance)
diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 1b24ef9f0e10..0d3f974c0724 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -283,7 +283,7 @@ def _open_code_with_warning(path):
class DocDescriptor:
"""Helper for builtins.open.__doc__
"""
- def __get__(self, obj, typ):
+ def __get__(self, obj, typ=None):
return (
"open(file, mode='r', buffering=-1, encoding=None, "
"errors=None, newline=None, closefd=True)\n\n" +
diff --git a/Lib/functools.py b/Lib/functools.py
index 9495fbe56eba..f87d9c571873 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -383,7 +383,7 @@ def _method(cls_or_self, /, *args, **keywords):
_method._partialmethod = self
return _method
- def __get__(self, obj, cls):
+ def __get__(self, obj, cls=None):
get = getattr(self.func, "__get__", None)
result = None
if get is not None:
@@ -888,7 +888,7 @@ def register(self, cls, method=None):
"""
return self.dispatcher.register(cls, func=method)
- def __get__(self, obj, cls):
+ def __get__(self, obj, cls=None):
def _method(*args, **kwargs):
method = self.dispatcher.dispatch(args[0].__class__)
return method.__get__(obj, cls)(*args, **kwargs)
@@ -926,7 +926,7 @@ def __set_name__(self, owner, name):
f"({self.attrname!r} and {name!r})."
)
- def __get__(self, instance, owner):
+ def __get__(self, instance, owner=None):
if instance is None:
return self
if self.attrname is None:
diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index c6771ce5291a..89312f18c967 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -2804,7 +2804,7 @@ class PropertyMock(Mock):
def _get_child_mock(self, /, **kwargs):
return MagicMock(**kwargs)
- def __get__(self, obj, obj_type):
+ def __get__(self, obj, obj_type=None):
return self()
def __set__(self, obj, val):
self(val)
diff --git a/Tools/demo/eiffel.py b/Tools/demo/eiffel.py
index 736abea81738..a76c2324dd6a 100755
--- a/Tools/demo/eiffel.py
+++ b/Tools/demo/eiffel.py
@@ -78,7 +78,7 @@ def __init__(self, func, pre, post):
self.__name__ = func.__name__
self.__doc__ = func.__doc__
- def __get__(self, obj, cls):
+ def __get__(self, obj, cls=None):
return EiffelMethodWrapper(obj, self)
def callmethod(self, inst, args, kwargs):
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