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...issubclass The new syntax should be accepted for calls to isinstance and issubclass as long as the Union items are valid arguments to isinstance and issubclass themselves. # valid isinstance("", int | str) # invalid isinstance(2, list[int]) # TypeError: isinstance() argument 2 cannot be a parameterized generic isinstance(1, int | list[int]) # valid issubclass(bool, int | float) # invalid issubclass(bool, bool | list[int]) Incompatible changes In some situations, some exceptions will not ...
...issubclass(list, Sequence) issubclass(list, MutableSequence) isinstance((), Sequence) not issubclass(tuple, MutableSequence) isinstance("", Sequence) issubclass(bytearray, MutableSequence) The primary mechanism proposed here is to allow overloading the built-in functions isinstance() and issubclass(). The overloading works as follows: The call isinstance(x, C) first checks whether C.__instancecheck__ exists, and if so, calls C.__instancecheck__(x) instead of its normal implementation. Similarl...
...issubclass, the new optional syntax should be supported in both isinstance and issubclass, isinstance(1, int?) # true issubclass(Child, Super?) # true A new dunder method will need to be implemented to allow the ? operator to be overloaded for other functionality. Backwards Compatibility ? is currently unused in Python syntax, therefore this PEP is fully backwards compatible. Reference Implementation A reference implementation can be found here [5]. Rejected Ideas Discussed alternatives ...
...issubclass(list, list[str]) TypeError: issubclass() arg 2 cannot be a parameterized generic >>> isinstance(list[str], types.GenericAlias) True Objects created with bare types and parameterized types are exactly the same. The generic parameters are not preserved in instances created with parameterized types, in other words generic types erase type parameters during object creation. One important consequence of this is that the interpreter does not attempt to type check operations on th...
...issubclass(D, C) returns true iff class D is derived from class C, directly or indirectly. issubclass(C, C) always returns true. Both arguments must be class objects. isinstance(x, C) returns true iff x is an instance of C or of a (direct or indirect) subclass of C. The first argument may hyave any type; if x is not an instance of any class, isinstance(x, C) always returns false. The second argument must be a class object. Sequence Unpacking Previous Python versions...
...issubclass(cls, collections.abc.Mapping) is true will have __match_container__ set to MATCH_MAPPING. All other standard library classes for which issubclass(cls, collections.abc.Sequence) is true will have __match_container__ set to MATCH_SEQUENCE. For the following builtin classes __match_class__ will be set to MATCH_SELF: bool bytearray bytes float frozenset int set str list tuple dict Legal optimizations The above semantics implies a lot of redundant effort and copying in the implementat...
...issubclass() can be used only with non-data protocols. This restriction exists because some data attributes can be set on an instance in constructor and this information is not always available on the class object. Type checkers should reject an isinstance() or issubclass() call, if there is an unsafe overlap between the type of the first argument and the protocol. Type checkers should be able to select a correct element from a union after a safe isinstance() or issubclass() call. For narrowing ...
...issubclass(). (Yet. It was done to issubclass() in Python 2.3.) Introspecting instances of built-in types For instances of built-in types (and for new-style classes in general), x.__class__ is now the same as type(x): >>> type([]) <type 'list'> >>> [].__class__ <type 'list'> >>> list <type 'list'> >>> isinstance([], list) 1 >>> isinstance([], dict) 0 >>> isinstance([], object) 1 >>> In classic Python, the method names of lists were available as the __m...
...issubclass built-in functions. NOTE: These two method names are reserved for use by the typing module and the generic types machinery, and any other use is discouraged. The reference implementation (with tests) can be found in [4], and the proposal was originally posted and discussed on the typing tracker, see [5]. Dynamic class creation and types.resolve_bases type.__new__ will not perform any MRO entry resolution. So that a direct call type('Tokens', (List[int],), {}) will fail. This is done...
...issubclass(cls, abc) returns True for the class itself but returns False for all its direct base classes. Implicit ABCs for a given class (either registered or inferred from the presence of a special method like __len__()) are inserted directly after the last ABC explicitly listed in the MRO of said class. In its most basic form, this linearization returns the MRO for the given type: >>> _compose_mro(dict, []) [<class 'dict'>, <class 'object'>] When the second argument con...
...issubclass(D,C), so it "works": super(C, self).meth() Proposal: Add a __class__ keyword which refers to the class currently being defined (executed). (But see open issues.) class C(B): def meth(self): super(__class__, self).meth() Note that super calls may be further simplified by the "New Super" PEP (Spealman). The __class__ (or __this_class__) attribute came up in attempts to simplify the explanation and/or implementation of that PEP, but was separated out as an indepe...
...issubclass(x.__class__, X) but not issubclass(type(x), X). isinstance(x, X): if X is a new-style class, this is now equivalent to issubclass(type(x), X) or issubclass(x.__class__, X). Previously only type(x) was tested. (For classic classes this was already the case.) compile(), eval() and the exec statement now fully support source code passed as unicode strings. int subclasses can be initialized with longs if the value fits in an int. See SF bug #683467. long(string, base) takes time linear ...
...issubclass and isinstance. All type information in instances is erased at runtime. Examples: def count(seq: Sequence) -> int: # Same as Sequence[Any] ... class FrameworkBase(Generic[S, T]): ... class UserClass: ... issubclass(UserClass, FrameworkBase) # This is OK class Node(Generic[T]): ... IntNode = Node[int] my_node = IntNode() # at runtime my_node.__class__ is Node # inferred static type of my_node is Node[int] Covariance and Contravaria...
...issubclass(M, M1) and issubclass(M, M2). (This is because a method of B1 should be able to call a meta-method defined in M1 on self.__class__, even when self is an instance of a subclass of B1.) The metaclasses book describes a mechanism whereby a suitable metaclass is automatically created, when necessary, through multiple inheritance from M1 and M2. In Python 2.2, I have chosen a simpler approach which raises an exception if the metaclass constraint is not satisfied; it is up to th...
...issubclass and also try/except constructs. Proposal It is suggested that to fix this situation all that is needed is a simple change to the way the -m option is implemented: in addition to binding the module object to sys.modules['__main__'], it is also bound to sys.modules['module.name']. Nick Coghlan has suggested that this is as simple as modifying the runpy module's _run_module_as_main function as follows: main_globals = sys.modules["__main__"].__dict__ to instead be: main_module = sys...
...issubclass() by 50-70%, so as to match Python 2.5 speed despite the __instancecheck__ / __subclasscheck__ mechanism. In the process, fix a bug where isinstance() and issubclass(), when given a tuple of classes as second argument, were looking up __instancecheck__ / __subclasscheck__ on the tuple rather than on each type object. Issue #3663: Py_None was decref'd when printing SyntaxErrors. Issue #3651: Fix various memory leaks when using the buffer interface, or when the "s#" code of Py...
...issubclass(methclass, klass): raise AccessViolation # If we got here, it must be okay to access the attribute if args: return setattr(self, name, *args) return obj # tests class A(Access): def __init__(self, foo=0, name='A'): self._foo = foo # can't set private names in __init__ self.__initprivate(name) def __initprivate(self, name): self._na...
...issubclass(), the dict method has_key(), the string and unicode methods endswith(), isalnum(), isalpha(), isdigit(), islower(), isspace(), istitle(), isupper(), and startswith(), the unicode methods isdecimal() and isnumeric(), and the 'closed' attribute of file objects. The predicates in the operator module are also changed to return a bool, including operator.truth(). Because bool inherits from int, True+1 is valid and equals 2, and so on. This is important for backwards compatibility: becau...