How to specify the type of pandas series elements in type hints?

Question

My function returns a pandas series, where all elements have a specific type (say str). The following MWE should give an impression:

import pandas as pd 
def f() -> pd.Series:
    return pd.Series(['a', 'b']) 

Within the type hints I want to make clear, that f()[0] will always be of type str (compared for example to a function that would return pd.Series([0, 1])). My initial guess was to use def f() -> pd.Series[str]: what gives the TypeError: 'type' object is not subscriptable.

So, how to specify the type of pandas series elements in type hints?

Answer 1

您可以用于pandera类型提示和验证数据帧和系列：https://pandera.readthedocs.io/en/stable/schema_models.html#schema-models

所以在这种情况下：

from pandera.typing import Series
import pandas as pd 

def f() -> Series[str]:
    return pd.Series(['a', 'b']) 

Answer 2

对于 python 3.8 尝试：

def f() -> "pd.Series[str]":
    pass

或者：

f_return_type = "pd.Series[str]"
def f() -> f_return_type:
    pass

或# type: pd.Series[str]对于变量

Answer 3

不幸的是，Python 的类型提示不支持现成的。尽管如此，您始终可以使用dataenforce库（链接）来添加提示甚至强制验证。