如果我将默认设置为 None，我可以省略 Optional 吗？
Can I omit Optional if I set default to None?
例如：
def foo(bar: int = None):
pass
当我检查 bar 的 type/annotation 时，pycharm 告诉我它是 Optional[int]。
bar: int = None 看起来比 bar: Optional[int] = None 干净得多，尤其是当您有 10 个以上参数时。
那么我可以简单地省略 Optional 吗？像 mypy 或其他 linters 这样的工具会将这种情况突出显示为 en 错误吗？
看起来 python 本身不喜欢这个想法：
In [1]: from typing import Optional
In [2]: from inspect import signature
In [3]: def foo(a: int = None): pass
In [4]: def bar(a: Optional[int] = None): pass
In [5]: signature(foo).parameters['a'].annotation
Out[5]: int
In [6]: signature(bar).parameters['a'].annotation
Out[6]: typing.Union[int, NoneType]
没有。以前允许省略 Optional，但后来被删除了。
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.
某些工具可能仍会为旧版支持提供旧行为。即使是这样，也不要指望它在未来得到支持。
具体而言，mypy 默认仍然支持隐式 Optional，但明确指出这可能会在未来发生变化：
Optional types and the None type (mypy v0.782)
[...] You can use the --no-implicit-optional command-line option to stop treating arguments with a None default value as having an implicit Optional[...] type. It’s possible that this will become the default behavior in the future.
中跟踪此行为的弃用
PEP 484 中定义的标准的先前版本允许这样做。
但是，最新版本在 Union section 中声明如下：
A past version of this PEP allowed type checkers to assume an optional
type when the default value is None, as in this code:
def handle_employee(e: Employee = None): ...
This would have been treated as equivalent to:
def handle_employee(e: Optional[Employee] = None) -> None: ...
This is no longer the recommended behavior. Type checkers should move
towards requiring the optional type to be made explicit.
对此我很高兴。在我看来，它实际上看起来很刺耳。
例如：
def foo(bar: int = None):
pass
当我检查 bar 的 type/annotation 时，pycharm 告诉我它是 Optional[int]。
bar: int = None 看起来比 bar: Optional[int] = None 干净得多，尤其是当您有 10 个以上参数时。
那么我可以简单地省略 Optional 吗？像 mypy 或其他 linters 这样的工具会将这种情况突出显示为 en 错误吗？
看起来 python 本身不喜欢这个想法：
In [1]: from typing import Optional
In [2]: from inspect import signature
In [3]: def foo(a: int = None): pass
In [4]: def bar(a: Optional[int] = None): pass
In [5]: signature(foo).parameters['a'].annotation
Out[5]: int
In [6]: signature(bar).parameters['a'].annotation
Out[6]: typing.Union[int, NoneType]
没有。以前允许省略 Optional，但后来被删除了。
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.
某些工具可能仍会为旧版支持提供旧行为。即使是这样，也不要指望它在未来得到支持。
具体而言，mypy 默认仍然支持隐式 Optional，但明确指出这可能会在未来发生变化：
中跟踪此行为的弃用Optional types and the None type (mypy v0.782)
[...] You can use the
--no-implicit-optionalcommand-line option to stop treating arguments with a None default value as having an implicit Optional[...] type. It’s possible that this will become the default behavior in the future.
PEP 484 中定义的标准的先前版本允许这样做。
但是，最新版本在 Union section 中声明如下：
A past version of this PEP allowed type checkers to assume an optional type when the default value is None, as in this code:
def handle_employee(e: Employee = None): ...This would have been treated as equivalent to:
def handle_employee(e: Optional[Employee] = None) -> None: ...This is no longer the recommended behavior. Type checkers should move towards requiring the optional type to be made explicit.
对此我很高兴。在我看来，它实际上看起来很刺耳。