Backport removal of BidirectionalMapping.__subclasshook__ to Python 2…

…-compatible 0.18.x branch

CHANGELOG.rst

@@ -26,6 +26,14 @@ click "`Watch <https://help.github.com/en/articles/watching-and-unwatching-relea
 and choose "Releases".
 
 
+0.18.4 (2020-11-02)
+-------------------
+
+- Backport fix from v0.20.0
+  that removes :meth:`bidict.BidirectionalMapping.__subclasshook__`
+  due to lack of use and maintenance cost.
+
+
 0.18.3 (2019-09-22)
 -------------------
 

bidict/_abc.py

@@ -39,11 +39,6 @@ class BidirectionalMapping(Mapping):  # pylint: disable=abstract-method,no-init
     which implementors of :class:`BidirectionalMapping`
     should override to return a reference to the inverse
     :class:`BidirectionalMapping` instance.
-
-    Implements :attr:`__subclasshook__` such that any
-    :class:`~collections.abc.Mapping` that also provides
-    :attr:`~BidirectionalMapping.inverse`
-    will be considered a (virtual) subclass of this ABC.
     """
 
     __slots__ = ()
@@ -79,25 +74,6 @@ def __inverted__(self):
         """
         return iteritems(self.inverse)
 
-    @classmethod
-    def __subclasshook__(cls, C):  # noqa: N803 (argument name should be lowercase)
-        """Check if *C* is a :class:`~collections.abc.Mapping`
-        that also provides an ``inverse`` attribute,
-        thus conforming to the :class:`BidirectionalMapping` interface,
-        in which case it will be considered a (virtual) C
-        even if it doesn't explicitly extend it.
-        """
-        if cls is not BidirectionalMapping:  # lgtm [py/comparison-using-is]
-            return NotImplemented
-        if not Mapping.__subclasshook__(C):
-            return NotImplemented
-        mro = getattr(C, '__mro__', None)
-        if mro is None:  # Python 2 old-style class
-            return NotImplemented
-        if not any(B.__dict__.get('inverse') for B in mro):
-            return NotImplemented
-        return True
-
 
 #                             * Code review nav *
 #==============================================================================

bidict/_base.py

@@ -46,14 +46,6 @@
 _NODUP = _DedupResult(False, False, _MISS, _MISS)
 
 
-# Since BidirectionalMapping implements __subclasshook__, and BidictBase
-# provides all the required attributes that the __subclasshook__ checks for,
-# BidictBase would be a (virtual) subclass of BidirectionalMapping even if
-# it didn't subclass it explicitly. But subclassing BidirectionalMapping
-# explicitly allows BidictBase to inherit any useful implementations that
-# BidirectionalMapping provides that aren't part of the required interface,
-# such as its `__inverted__` implementation and `inverse` alias.
-
 class BidictBase(BidirectionalMapping):
     """Base class implementing :class:`BidirectionalMapping`."""
 

setup.py

@@ -44,7 +44,7 @@
 # Manually keep these version pins in sync with those in .travis.yml and .pre-commit-config.yaml.
 
 SETUP_REQS = [
-    'setuptools_scm < 4',
+    'setuptools_scm',
 ]
 
 SPHINX_REQS = [
@@ -81,10 +81,8 @@
 FLAKE8_REQ = 'flake8 < 3.8'
 PYDOCSTYLE_REQ = 'pydocstyle < 3.1'
 PYLINT_REQS = [
-    # Pin to exact versions of Pylint and Astroid, which don't follow semver.
-    # See https://github.com/PyCQA/astroid/issues/651#issuecomment-469021040
-    'pylint == 2.2.3',
-    'astroid == 2.1.0',
+    'pylint',
+    'astroid',
 ]
 
 LINT_REQS = [

tests/conftest.py

@@ -8,14 +8,13 @@
 """Set up hypothesis."""
 
 from os import getenv
-from hypothesis import HealthCheck, settings, unlimited
+from hypothesis import HealthCheck, settings
 
 
 MAX_EXAMPLES_DEFAULT = 200
 SETTINGS = {
     'max_examples': int(getenv('HYPOTHESIS_MAX_EXAMPLES') or MAX_EXAMPLES_DEFAULT),
     'deadline': None,
-    'timeout': unlimited,
     'suppress_health_check': (HealthCheck.too_slow,),
 }
 settings.register_profile('custom', **SETTINGS)

tests/test_class_relationships.py

@@ -11,6 +11,7 @@
     from collections.abc import Hashable
 except ImportError:  # Python < 3
     from collections import Hashable
+from collections import OrderedDict
 
 import pytest
 
@@ -22,19 +23,6 @@ class OldStyleClass:  # pylint: disable=no-init,too-few-public-methods
     """In Python 2 this is an old-style class (not derived from object)."""
 
 
-class VirtualBimapSubclass(Mapping):  # pylint: disable=abstract-method
-    """Dummy type that implements the BidirectionalMapping interface
-    without explicitly extending it, and so should still be considered a
-    (virtual) subclass if the BidirectionalMapping ABC is working correctly.
-    (See :meth:`BidirectionalMapping.__subclasshook__`.)
-
-    (Not actually a *working* BidirectionalMapping implementation,
-    but doesn't need to be for the purposes of this test.)
-    """
-
-    inverse = NotImplemented
-
-
 class AbstractBimap(BidirectionalMapping):  # pylint: disable=abstract-method
     """Dummy type that explicitly extends BidirectionalMapping
     but fails to provide a concrete implementation for the
@@ -51,19 +39,16 @@ class AbstractBimap(BidirectionalMapping):  # pylint: disable=abstract-method
 
 
 BIDICT_TYPES = (bidict, frozenbidict, FrozenOrderedBidict, OrderedBidict)
-BIMAP_TYPES = BIDICT_TYPES + (VirtualBimapSubclass, AbstractBimap)
-NOT_BIMAP_TYPES = (dict, object, OldStyleClass)
+BIMAP_TYPES = BIDICT_TYPES + (AbstractBimap,)
+NOT_BIMAP_TYPES = (dict, OrderedDict, int, object, OldStyleClass)
 MUTABLE_BIDICT_TYPES = (bidict, OrderedBidict)
 HASHABLE_BIDICT_TYPES = (frozenbidict, FrozenOrderedBidict)
 ORDERED_BIDICT_TYPES = (OrderedBidict, FrozenOrderedBidict)
 
 
 @pytest.mark.parametrize('bi_cls', BIMAP_TYPES)
 def test_issubclass_bimap(bi_cls):
-    """All bidict types should subclass :class:`BidirectionalMapping`,
-    and any class conforming to the interface (e.g. VirtualBimapSubclass)
-    should be considered a (virtual) subclass too.
-    """
+    """All bidict types should be considered subclasses of :class:`BidirectionalMapping`."""
     assert issubclass(bi_cls, BidirectionalMapping)
 
 
@@ -127,6 +112,11 @@ def test_issubclass_internal():
     assert not issubclass(frozenbidict, OrderedBidict)
     assert not issubclass(frozenbidict, bidict)
 
+    # Regression test for #111, Bug in BidirectionalMapping.__subclasshook__():
+    # Any class with an inverse attribute is considered a collections.abc.Mapping
+    OnlyHasInverse = type('OnlyHasInverse', (), {'inverse': Ellipsis})
+    assert not issubclass(OnlyHasInverse, Mapping)
+
 
 def test_abstract_bimap_init_fails():
     """See the :class:`AbstractBimap` docstring above."""