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 returnpd.Series([0, 1])). I did this:

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

But

TypeError: 'type' object is not subscriptable

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

Answer 1

You can utilize typing.TypeVar to accomplish this:

from typing import (
    TypeVar
)

SeriesString = TypeVar('pandas.core.series.Series(str)')
def f() -> SeriesString:

Answer 2

Unfortunately Python's type hinting does not support this out of the shelf. Nonetheless, you can always make use of dataenforce library (link) to add hints or even enforce validation.