我是Python3中静态类型提示的铁杆粉丝和倡导者,我已经使用它们一段时间了,没有遇到任何问题。
我刚刚遇到了一个新的边缘情况,我似乎不能编译。如果我想定义一个自定义类型,然后定义它的参数,该怎么办?
例如,这在Python 3中很常见:
from typing import List, NewType
CustomObject = NewType('CustomObject', List[int])
def f(data: List[CustomObject]):
# do something
但这不会编译:
class MyContainer():
# some class definition ...
from typing import NewType
SpecialContainer = NewType('SpecialContainer', MyContainer)
def f(data: SpecialContainer[str]):
# do something
我意识到在这种情况下,从技术上讲,SpecialContainer
是一个函数,但它不应该作为类型签名上下文中的函数来计算。第二个代码片段因TypeError: 'function' object is not subscriptable
而失败。
发布于 2018-09-04 01:44:44
编译我的代码示例
你必须从头开始设计你的类来接受静态类型提示。这不符合我最初的用例,因为我试图声明第三方类的特殊子类型,但它编译了我的代码样本。
from typing import Generic, TypeVar, Sequence, List
# Declare your own accepted types for your container, required
T = TypeVar('T', int, str, float)
# The custom container has be designed to accept types hints
class MyContainer(Sequence[T]):
# some class definition ...
# Now, you can make a special container type
# Note that Sequence is a generic of List, and T is a generic of str, as defined above
SpecialContainer = TypeVar('SpecialContainer', MyContainer[List[str]])
# And this compiles
def f(data: SpecialContainer):
# do something
子类型化第三方类
我的初衷是创建一个类型提示,用于解释函数f()
如何接受一个pd.DataFrame
对象,该对象由整数索引,并且其单元格都是字符串。使用上面的答案,我想出了一个人为的方式来表达这一点。
from typing import Mapping, TypeVar, NewType, NamedTuple
from pandas import pd
# Create custom types, required even if redundant
Index = TypeVar('Index')
Row = TypeVar('Row')
# Create a child class of pd.DataFrame that includes a type signature
# Note that Mapping is a generic for a key-value store
class pdDataFrame(pd.DataFrame, Mapping[Index, Row]):
pass
# Now, this compiles, and explains what my special pd.DataFrame does
pdStringDataFrame = NewType('pdDataFrame', pdDataFrame[int, NamedTuple[str]])
# And this compiles
def f(data: pdStringDataFrame):
pass
这值得吗?
Sequence
、Mapping
或Any
,那么请使用它。您可以自由地将类型变量添加到您的类definition.- Try using an existing type variable to get your point across, e.g. `MyOrderedDictType = NewType('MyOrderedDictType', Dict[str, float])`
- If that doesn't work, you'll have to clutter your namespace with trivial child classes and type variables to get the type hint to compile. Better to use a docstring or comment to explain your situation.
https://stackoverflow.com/questions/52153879
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