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Merged
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Oct 21, 2016
Merged

A real fix for issue #250 (failure with mock) #295

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b07b8ea
A real fix for #250
ilevkivskyi Oct 9, 2016
eb7801b
Use _gorg for the case of multiply parameterized generics
ilevkivskyi Oct 9, 2016
be5d7ed
Formatting
ilevkivskyi Oct 9, 2016
63482fa
Response to comments + some tests
ilevkivskyi Oct 10, 2016
307bf64
Add tests illustrating new dunder attributes; preserve initial class …
ilevkivskyi Oct 16, 2016
f4932bb
Response to comments
ilevkivskyi Oct 20, 2016
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43 changes: 42 additions & 1 deletion python2/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -603,13 +603,54 @@ def test_orig_bases(self):
class C(typing.Dict[str, T]): pass
self.assertEqual(C.__orig_bases__, (typing.Dict[str, T],))

def test_naive_runtime_checks(self):
def naive_dict_check(obj, tp):
# Check if a dictionary conforms to Dict type
if len(tp.__parameters__) > 0:
return NotImplemented
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NotImplemented is not a great value to return here -- it's really only supposed to be used by binary operators (e.g. __add__) to indicate that the reverse variant should be tried (i.e. __radd__). Maybe raising NotImplementedError would be better?

While this is just a test, it will be used as an example and copied, and raising makes it clearer that that's an unimplemented feature of the naive check.

if tp.__args__:
KT, VT = tp.__args__
return all(isinstance(k, KT) and isinstance(v, VT)
for k, v in obj.items())
self.assertTrue(naive_dict_check({'x': 1}, typing.Dict[typing.Text, int]))
self.assertFalse(naive_dict_check({1: 'x'}, typing.Dict[typing.Text, int]))
self.assertIs(naive_dict_check({1: 'x'}, typing.Dict[typing.Text, T]), NotImplemented)

def naive_generic_check(obj, tp):
# Check if an instance conforms to the generic class
if not hasattr(obj, '__orig_class__'):
return NotImplemented
return obj.__orig_class__ == tp
class Node(Generic[T]): pass
self.assertTrue(naive_generic_check(Node[int](), Node[int]))
self.assertFalse(naive_generic_check(Node[str](), Node[int]))
self.assertFalse(naive_generic_check(Node[str](), List))
self.assertIs(naive_generic_check([1,2,3], Node[int]), NotImplemented)

def naive_list_base_check(obj, tp):
# Check if list conforms to a List subclass
return all(isinstance(x, tp.__orig_bases__[0].__args__[0])
for x in obj)
class C(List[int]): pass
self.assertTrue(naive_list_base_check([1, 2, 3], C))
self.assertFalse(naive_list_base_check(['a', 'b'], C))

def test_multi_subscr_base(self):
T = TypeVar('T')
U = TypeVar('U')
V = TypeVar('V')
# these should just work
class C(List[T][U][V]): pass
class D(C, List[T][U][V]): pass
self.assertEqual(C.__parameters__, (V,))
self.assertEqual(D.__parameters__, (V,))
self.assertEqual(C[int].__parameters__, ())
self.assertEqual(D[int].__parameters__, ())
self.assertEqual(C[int].__args__, (int,))
self.assertEqual(D[int].__args__, (int,))
self.assertEqual(C.__bases__, (List,))
self.assertEqual(D.__bases__, (C, List))
self.assertEqual(C.__orig_bases__, (List[T][U][V],))
self.assertEqual(D.__orig_bases__, (C, List[T][U][V]))

def test_pickle(self):
global C # pickle wants to reference the class by name
Expand Down
14 changes: 9 additions & 5 deletions python2/typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1045,7 +1045,7 @@ class GenericMeta(TypingMeta, abc.ABCMeta):
"""Metaclass for generic types."""

def __new__(cls, name, bases, namespace,
tvars=None, args=None, origin=None, extra=None):
tvars=None, args=None, origin=None, extra=None, orig_bases=None):
if tvars is not None:
# Called from __getitem__() below.
assert origin is not None
Expand Down Expand Up @@ -1086,7 +1086,7 @@ def __new__(cls, name, bases, namespace,
", ".join(str(g) for g in gvars)))
tvars = gvars

orig_bases = bases
initial_bases = bases
if extra is None:
extra = namespace.get('__extra__')
if extra is not None and type(extra) is abc.ABCMeta and extra not in bases:
Expand All @@ -1104,8 +1104,9 @@ def __new__(cls, name, bases, namespace,
self.__extra__ = extra
# Speed hack (https://github.com/python/typing/issues/196).
self.__next_in_mro__ = _next_in_mro(self)
if origin is None:
self.__orig_bases__ = orig_bases
# Preserve base classes on subclassing (__bases__ are type erased now).
if orig_bases is None:
self.__orig_bases__ = initial_bases

# This allows unparameterized generic collections to be used
# with issubclass() and isinstance() in the same way as their
Expand Down Expand Up @@ -1193,7 +1194,8 @@ def __getitem__(self, params):
tvars=tvars,
args=args,
origin=self,
extra=self.__extra__)
extra=self.__extra__,
orig_bases=self.__orig_bases__)

def __instancecheck__(self, instance):
# Since we extend ABC.__subclasscheck__ and
Expand Down Expand Up @@ -1240,6 +1242,8 @@ def __new__(cls, *args, **kwds):
else:
origin = _gorg(cls)
obj = cls.__next_in_mro__.__new__(origin)
if '__dict__' in cls.__dict__:
obj.__orig_class__ = cls
obj.__init__(*args, **kwds)
return obj

Expand Down
44 changes: 43 additions & 1 deletion src/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -630,13 +630,55 @@ def test_orig_bases(self):
class C(typing.Dict[str, T]): ...
self.assertEqual(C.__orig_bases__, (typing.Dict[str, T],))
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I know there are no docs for __parameters__ etc. either, but I would still like to see some kind of example code that takes a class like this and recovers what it means given the various new dunder methods (__origin__, __orig_bases__, __parameters__). E.g. if I had a dict {x: y} how would I check that it's a subclass of Dict[str, T]? (The answer should reveal that the type of x must be str and T must be the type of y.)

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It is quite difficult to write a reasonable runtime type check functions. I just added three naive functions just to illustrate how to use the dunder attributes for typical type checking tasks.

In process of doing this I realized that it is difficult to perform runtime type checks since type erasure happens not only at subclassing, but also at generic class instantiation. In the new commit I added __orig_class__ to instances (if subclass allows this, i.e., it does not use __slots__) that saves a reference to original class before type erasure.
So that now Node[int]().__class__ is Node, while Node[int]().__orig_class__ is Node[int].


def test_naive_runtime_checks(self):
def naive_dict_check(obj, tp):
# Check if a dictionary conforms to Dict type
if len(tp.__parameters__) > 0:
return NotImplemented
if tp.__args__:
KT, VT = tp.__args__
return all(isinstance(k, KT) and isinstance(v, VT)
for k, v in obj.items())
self.assertTrue(naive_dict_check({'x': 1}, typing.Dict[str, int]))
self.assertFalse(naive_dict_check({1: 'x'}, typing.Dict[str, int]))
self.assertIs(naive_dict_check({1: 'x'}, typing.Dict[str, T]), NotImplemented)

def naive_generic_check(obj, tp):
# Check if an instance conforms to the generic class
if not hasattr(obj, '__orig_class__'):
return NotImplemented
return obj.__orig_class__ == tp
class Node(Generic[T]): ...
self.assertTrue(naive_generic_check(Node[int](), Node[int]))
self.assertFalse(naive_generic_check(Node[str](), Node[int]))
self.assertFalse(naive_generic_check(Node[str](), List))
self.assertIs(naive_generic_check([1,2,3], Node[int]), NotImplemented)

def naive_list_base_check(obj, tp):
# Check if list conforms to a List subclass
return all(isinstance(x, tp.__orig_bases__[0].__args__[0])
for x in obj)
class C(List[int]): ...
self.assertTrue(naive_list_base_check([1, 2, 3], C))
self.assertFalse(naive_list_base_check(['a', 'b'], C))

def test_multi_subscr_base(self):
T = TypeVar('T')
U = TypeVar('U')
V = TypeVar('V')
# these should just work
class C(List[T][U][V]): ...
class D(C, List[T][U][V]): ...
self.assertEqual(C.__parameters__, (V,))
self.assertEqual(D.__parameters__, (V,))
self.assertEqual(C[int].__parameters__, ())
self.assertEqual(D[int].__parameters__, ())
self.assertEqual(C[int].__args__, (int,))
self.assertEqual(D[int].__args__, (int,))
self.assertEqual(C.__bases__, (List,))
self.assertEqual(D.__bases__, (C, List))
self.assertEqual(C.__orig_bases__, (List[T][U][V],))
self.assertEqual(D.__orig_bases__, (C, List[T][U][V]))


def test_pickle(self):
global C # pickle wants to reference the class by name
Expand Down
14 changes: 9 additions & 5 deletions src/typing.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -938,7 +938,7 @@ class GenericMeta(TypingMeta, abc.ABCMeta):
"""Metaclass for generic types."""

def __new__(cls, name, bases, namespace,
tvars=None, args=None, origin=None, extra=None):
tvars=None, args=None, origin=None, extra=None, orig_bases=None):
if tvars is not None:
# Called from __getitem__() below.
assert origin is not None
Expand Down Expand Up @@ -979,7 +979,7 @@ def __new__(cls, name, bases, namespace,
", ".join(str(g) for g in gvars)))
tvars = gvars

orig_bases = bases
initial_bases = bases
if extra is not None and type(extra) is abc.ABCMeta and extra not in bases:
bases = (extra,) + bases
bases = tuple(_gorg(b) if isinstance(b, GenericMeta) else b for b in bases)
Expand All @@ -995,8 +995,9 @@ def __new__(cls, name, bases, namespace,
self.__extra__ = extra
# Speed hack (https://github.com/python/typing/issues/196).
self.__next_in_mro__ = _next_in_mro(self)
if origin is None:
self.__orig_bases__ = orig_bases
# Preserve base classes on subclassing (__bases__ are type erased now).
if orig_bases is None:
self.__orig_bases__ = initial_bases

# This allows unparameterized generic collections to be used
# with issubclass() and isinstance() in the same way as their
Expand Down Expand Up @@ -1084,7 +1085,8 @@ def __getitem__(self, params):
tvars=tvars,
args=args,
origin=self,
extra=self.__extra__)
extra=self.__extra__,
orig_bases=self.__orig_bases__)

def __instancecheck__(self, instance):
# Since we extend ABC.__subclasscheck__ and
Expand Down Expand Up @@ -1128,6 +1130,8 @@ def __new__(cls, *args, **kwds):
else:
origin = _gorg(cls)
obj = cls.__next_in_mro__.__new__(origin)
if '__dict__' in cls.__dict__:
obj.__orig_class__ = cls
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I think I'd just catch AttributeError here -- the "dict in dict" idiom feels obscure.

obj.__init__(*args, **kwds)
return obj

Expand Down