According to Suggested syntax for Python 2.7 and straddling code in PEP 484 which defined type hinting, there is an alternative syntax for compatibility with Python 2.7. It is however not mandatory so I don’t know how well supported it is, but quoting the PEP: Some tools may want to support type annotations in code … 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
No. Omitting Optional was previously allowed, but has since been removed. A past version of this PEP allowed type checkers to assume an optional type when the default value is None […] This is no longer the recommended behavior. Type checkers should move towards requiring the optional type to be made explicit. Some tools may … Read more
Update Check recent numpy versions for a new typing module https://numpy.org/doc/stable/reference/typing.html#module-numpy.typing dated answer It looks like typing module was developed at: https://github.com/python/typing The main numpy repository is at https://github.com/numpy/numpy Python bugs and commits can be tracked at http://bugs.python.org/ The usual way of adding a feature is to fork the main repository, develop the feature till … Read more
There is no real difference between using a plain typing.Dict and dict, no. However, typing.Dict is a Generic type * that lets you specify the type of the keys and values too, making it more flexible: def change_bandwidths(new_bandwidths: typing.Dict[str, str], user_id: int, user_name: str) -> bool: As such, it could well be that at some … Read more
You can specify recursive types in the typing language by using type aliases and forward reference strings, Garthoks = Union[Garthok, Iterable[‘Garthoks’]] Note that recursive types are not yet supported by mypy. But it will likely be added eventually. Update 2020/9/14: Microsoft announces support for recursive types in Pyright/Pylance. Some types of forward references are handled … Read more
You can’t. A list is a mutable, variable length structure. If you need a fixed-length structure, use a tuple instead: Tuple[float, float, float, float, float, float, float, float, float, float] Or better still, use a named tuple, which has both indices and named attributes: class BunchOfFloats(NamedTuple): foo: float bar: float baz: float spam: float ham: … Read more
As pointed out by Blckknght, you and Stanislav Ivanov in the comments, you can use NamedTuple: from typing import NamedTuple class NameInfo(NamedTuple): name: str first_letter: str def get_info(name: str) -> NameInfo: return NameInfo(name=name, first_letter=name[0]) Starting from Python 3.8 you can use TypedDict which is more similar to what you want: from typing import TypedDict class … Read more
Type hinting can’t say anything about exceptions. They are entirely out of scope for the feature. You can still document the exception in the docstring however. From PEP 484 — Type Hints: Exceptions No syntax for listing explicitly raised exceptions is proposed. Currently the only known use case for this feature is documentational, in which … Read more
Use a generic type to indicate that you’ll be returning an instance of cls: from typing import Type, TypeVar T = TypeVar(‘T’, bound=’TrivialClass’) class TrivialClass: # … @classmethod def from_int(cls: Type[T], int_arg: int) -> T: # … return cls(…) Any subclass overriding the class method but then returning an instance of a parent class (TrivialClass … Read more