typehints

问题 This question already has answers here : Type hint for NumPy ndarray dtype? (4 answers) Closed 1 year ago . How can I type hint that a value being returned by a function is both an NumPy array and holds NumPy float32 data? I can specify that the returned value is an array using: def func() -> np.ndarray: ... However, this does not enforce the knowledge that it is a float32 array. I can specify that the returned value is of type float32 using: def func() -> np.float32: ... However, this does

问题 Let's say I have a simple function like this: def foo(a: Any): return a.bar + a.baz I would like to change the type hint from Any to one that requires (well, suggests, given that it is a type hint ) that a provides the bar and baz attributes. What should it be changed to? 回答1: This is exactly what Protocols are for. In short, Protocols let you use structural instead of nominal subtyping. With nominal subtyping, type A is a subtype of B if A explicitly inherits or extends B. With structural

问题 Let's say I have a simple function like this: def foo(a: Any): return a.bar + a.baz I would like to change the type hint from Any to one that requires (well, suggests, given that it is a type hint ) that a provides the bar and baz attributes. What should it be changed to? 回答1: This is exactly what Protocols are for. In short, Protocols let you use structural instead of nominal subtyping. With nominal subtyping, type A is a subtype of B if A explicitly inherits or extends B. With structural

问题 In Pycharm, the following code produces a warning: from typing import List list1: List[int] = [1, 2, 3] list2: List[str] = ["1", "2", "3"] list3: List[object] = list1 + list2 # ↳ Expected type List[int] (matched generic type List[_T]), # got List[str] instead. Why? Should I not be concatenating two lists of mixed, hinted types? 回答1: As requested in the comments, here are some reasons why type checkers don't allow this. The first reason is somewhat prosaic: the type signature of list.__add__

问题 How do I write the function declaration using Python type hints for function returning multiple return values? Is the below syntax allowed? def greeting(name: str) -> str, List[float], int : // do something return a,b,c 回答1: You can use a typing.Tuple type hint (to specify the type of the content of the tuple, if it is not necessary, the built-in class tuple can be used instead): from typing import Tuple def greeting(name: str) -> Tuple[str, List[float], int]: # do something return a, b, c

问题 How do I write the function declaration using Python type hints for function returning multiple return values? Is the below syntax allowed? def greeting(name: str) -> str, List[float], int : // do something return a,b,c 回答1: You can use a typing.Tuple type hint (to specify the type of the content of the tuple, if it is not necessary, the built-in class tuple can be used instead): from typing import Tuple def greeting(name: str) -> Tuple[str, List[float], int]: # do something return a, b, c

问题 You can mix types inside tuples or lists. Why can't you specify that in typing hints? >>> from typing import Tuple, List >>> t = ('a', 1) >>> l = ['a', 1] >>> t2: Tuple[str, int] = ('a', 1) >>> l2: List[str, int] = ['a', 1] TypeError: Too many parameters for typing.List; actual 2, expected 1 回答1: 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

问题 You can mix types inside tuples or lists. Why can't you specify that in typing hints? >>> from typing import Tuple, List >>> t = ('a', 1) >>> l = ['a', 1] >>> t2: Tuple[str, int] = ('a', 1) >>> l2: List[str, int] = ['a', 1] TypeError: Too many parameters for typing.List; actual 2, expected 1 回答1: 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

问题 Using python 3, one has the option to use typehints. My question is, if a function returns None, should one add this, or leave it blank. i.e. def hint(p:str) -> None: pass def no_hint(p:str): pass And which PEP addresses this? 回答1: Be explicit and always include -> None for functions that return None That's because otherwise, for functions that don't take arguments , the type checker will assume that you did not use type hints at all. For example, is def foo(): going to return None , or was

问题 Using python 3, one has the option to use typehints. My question is, if a function returns None, should one add this, or leave it blank. i.e. def hint(p:str) -> None: pass def no_hint(p:str): pass And which PEP addresses this? 回答1: Be explicit and always include -> None for functions that return None That's because otherwise, for functions that don't take arguments , the type checker will assume that you did not use type hints at all. For example, is def foo(): going to return None , or was