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...isinstance and 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 excep...
...isinstance() and issubclass(). This would be symmetrical to how list[str]() creates a regular list. This design was rejected because isinstance() and issubclass() checks with parameterized generics would read like element-by-element runtime type checks. The result of those checks would be surprising, for example: >>> isinstance([1, 2, 3], list[str]) True Note the object doesn't match the provided generic type but isinstance() still returns True because it only checks whether the obje...
...isinstance(node, (FunctionDef, ClassDef, Module)): raise TypeError("%r can't have docstrings" % node.__class__.__name__) if node.body and isinstance(node.body[0], Expr) and \ isinstance(node.body[0].value, Str): if clean: import inspect return inspect.cleandoc(node.body[0].value.s) return node.body[0].value.s Using assignment expression: def get_docstring(node, clean=True): if not isinstance(node, (Function...
...isinstance(x, str) for x in val) User-defined type guards can also be used to determine whether a dictionary conforms to the type requirements of a TypedDict. class Person(TypedDict): name: str age: int def is_person(val: dict) -> "TypeGuard[Person]": try: return isinstance(val["name"], str) and isinstance(val["age"], int) except KeyError: return False def print_age(val: dict): if is_person(val): print(f"Age: {val['age']}") else: pri...
...isinstance(dependencies, list): raise TypeError('Field `project.dependencies` must be an array') for i, entry in enumerate(dependencies, 1): if not isinstance(entry, str): raise TypeError(f'Dependency #{i} of field `project.dependencies` must be a string') try: Requirement(entry) except InvalidRequirement as e: raise ValueError(f'Dependency #{i} of field `project.dependencies` is invalid: {e}') return dependencies de...
...isinstance([], Sequence) 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...
...isinstance(o, P): return o.common_method_name(1) # Results in TypeError not caught # statically if o is an X instance. Another potentially problematic case is assignment of attributes after instantiation: class P(Protocol): x: int class C: def initialize(self) -> None: self.x = 0 c = C() isinstance(c, P) # False c.initialize() isinstance(c, P) # True def f(x: Union[P, int]) -> None: if isinstance(x, P): # S...
...isinstance(other, (set, frozenset, d_keys)): result = set() for item in other: if item in self: result.add(item) return result if not isinstance(other, d_items): return NotImplemented d = {} if len(other) < len(self): self, other = other, self for item in self: if item in other: key, value = item d[key] = value retu...
...isinstance(other, MyIntegral): return do_my_adding_stuff(self, other) elif isinstance(other, OtherTypeIKnowAbout): return do_my_other_adding_stuff(self, other) else: return NotImplemented def __radd__(self, other): if isinstance(other, MyIntegral): return do_my_adding_stuff(other, self) elif isinstance(other, OtherTypeIKnowAbout): return do_my_other_adding_stuff(other, self) elif isinstance(o...
...isinstance(exc, UnicodeError): return (u"", exc.end) else: raise TypeError("can't handle %s" % exc.__name__) def replace(exc): if isinstance(exc, UnicodeEncodeError): return ((exc.end-exc.start)*u"?", exc.end) elif isinstance(exc, UnicodeDecodeError): return (u"\\ufffd", exc.end) elif isinstance(exc, UnicodeTranslateError): return ((exc.end-exc.start)*u"\\ufffd", exc.end) else: raise TypeError("can't handle %s" % exc.__...
...isinstance($value, ClsName): FAIL Class pattern with a single positional pattern: case ClsName($VAR): translates to: $kind = type($value).__match_class__ if $kind == MATCH_SELF: if not isinstance($value, ClsName): FAIL $VAR = $value else: As other positional-only class pattern Positional-only class pattern: case ClsName($VARS): translates to: if not isinstance($value, ClsName): FAIL $attrs = ClsName.__match_args__ if len($attr) < len($VARS): raise TypeE...
...isinstance(initializer, int): # In 2.6, int -> (int, long) initializer = [0]*initializer elif isinstance(initializer, basestring): if isinstance(initializer, unicode): # In 3.0, "if True" if encoding is None: # In 3.0, raise TypeError("explicit encoding required") encoding = sys.getdefaultencoding() initializer = initializer.encode(encoding) initializer = [ord(c) for c in initializer] else: if enco...
...isinstance and 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 Discusse...
...isinstance(node, Num): return node.n $$match_4_0 = node if isinstance($$match_4_0, _ast.Add): a, b = $$match_4_0.left, $$match_4_0.right return calculate(a) + calculate(b) elif isinstance($$match_4_0, _ast.Sub): a, b = $$match_4_0.left, $$match_4_0.right return calculate(a) - calculate(b) elif isinstance($$match_4_0, _ast.Mul): a, b = $$match_4_0.left, $$match_4_0.right return calculate(a) * calculate(b) elif isinstance(...
...isinstance(other, bool): return bool(int(self) & int(other)) else: return int.__and__(self, other) __rand__ = __and__ def __or__(self, other): if isinstance(other, bool): return bool(int(self) | int(other)) else: return int.__or__(self, other) __ror__ = __or__ def __xor__(self, other): if isinstance(other, bool): return bool(int(self) ^ int(other)) else: return ...
...isinstance(node, Node): traverse_tree(node.left) traverse_tree(node.right) elif isinstance(node, Leaf): print(node.value) In many cases class patterns occur nested, as in the example given in the motivation: if (isinstance(node, BinOp) and node.op == "+" and isinstance(node.right, BinOp) and node.right.op == "*"): a, b, c = node.left, node.right.left, node.right.right # Handle a + b*c The class pattern lets you concisely specify both an instance che...
...isinstance(node, Node) and node.children == [LParen(), RParen()]: return True return (isinstance(node, Node) and len(node.children) == 3 and isinstance(node.children[0], Leaf) and isinstance(node.children[1], Node) and isinstance(node.children[2], Leaf) and node.children[0].value == "(" and node.children[2].value == ")") This example shows an example of finding out the "shape" of the data without doing significa...
...isinstance(r, (str, unicode)): raise TypeError('__str__ returned non-string') return r The following function would be added to the C API and would be the equivalent to the str() built-in (ideally it be called PyObject_Str, but changing that function could cause a massive number of compatibility problems): PyObject *PyString_New(PyObject *); A reference implementation is available on Sourceforge [1] as a patch. Backwards Compatibility Some code may require that str() returns a s...
...isinstance() tests such as isinstance(d, Movie). The reason is that there is no existing support for checking types of dictionary item values, since isinstance() does not work with many PEP 484 types, including common ones like List[str]. This would be needed for cases like this: class Strings(TypedDict): items: List[str] print(isinstance({'items': [1]}, Strings)) # Should be False print(isinstance({'items': ['x']}, Strings)) # Should be True The above use case is not supported. Thi...
...isinstance' (the built-in class "basestring" exists specifically to let you use 'isinstance' to check if an object "is a [built-in] string"). Neither approach is easily and generally extensible to other protocols, defined by applications and third party frameworks, outside of the standard Python core. Even more important than checking if an object already supports a given protocol can be the task of obtaining a suitable adapter (wrapper or proxy) for the object, if the support is not already th...