Checking if a variable conforms to a typing object To check if string_list conforms to string_list_class, you can use the typeguard type checking library. from typeguard import check_type try: check_type(‘string_list’, string_list, string_list_class) print(“string_list conforms to string_list_class”) except TypeError: print(“string_list does not conform to string_list_class”) Checking the generic type of a typing object To check if … Read more
I’d recommend using a combination of TypeVar, to indicate that your self.o value could be any arbitrary type, and Type, in the following way: from typing import TypeVar, Type T = TypeVar(‘T’) class MyObj: def __init__(self, o: T) -> None: self.o = o def get_obj_class(self) -> Type[T]: return type(self.o) def accept_int_class(x: Type[int]) -> None: pass … Read more
In Python 3.5, you have to write self.some_attribute = None # type: AnotherClass Since Python 3.6, new type hinting syntax was added for variables (PEP 526): self.some_attribute: AnotherClass = None This will probably make every type-checking system complain, because None is in fact not an instance of AnotherClass. Instead, you can use typing.Union[None, AnotherClass], or … Read more
typing.get_type_hints is another method that doesn’t involve accessing magic properties directly: from typing import get_type_hints class Person: name: str age: int get_type_hints(Person) # returns {‘name’: <class ‘str’>, ‘age’: <class ‘int’>}
Figured it out: connection_string: str = “sqlite:///:memory:” engine = create_engine(connection_string) session = Session(bind=engine) print(type(engine)) # sqlalchemy.engine.base.Engine print(type(session)) # sqlalchemy.orm.session.Session Thus, type hinting is achieved the following way for example: from sqlalchemy.engine.base import Engine def test_func(engine: Engine): pass
In type theory, a list is a homogenous structure containing values of one type. As such, List only takes a single type, and every element of that list has to have that type. However, type theory also provides sum types, which you can think of as a wrapper around exactly one value selected from some … Read more
How about this, as a workaround? from typing import Optional, TYPE_CHECKING if TYPE_CHECKING: class Foo: pass else: Foo = type(‘Foo’, (), {}) Bar = Optional[Foo] typing.TYPE_CHECKING is a constant that will always be True at compile-time, and will always be False at runtime. In this way, we can keep MyPy happy by only telling it … Read more
As far as I am concerned, there is no such direct tool in PyCharm. There are, however, 3rd party tools for this. .pyi generators MyPy Yes, I guess anyone who wants to use compile-time type checking in Python, probably ends up using MyPy. MyPy contains stubgen.py tool which generates .pyi files. Usage mkdir out stubgen … Read more
You may think of the typing library as a specification on how to declare certain types. If something is not defined in that specification then it’s always better assume it to be an undefined behavior. However in the particular case of Python and typing we have a kind-of-reference static type checker which is mypy. So … Read more
The way named tuples are constructed make inheritance from typing.NamedTuple classes as yet not possible. You’d have to write your own metaclass to extend the typing.NamedTupleMeta class to make subclassing work, and even then the class generated by collections.namedtuple() is just not built to extend. Instead, you want to use the new dataclasses module to … Read more