Pythonic type hints with pandas?

问题

Let's take a simple function that takes a str and returns a dataframe:

import pandas as pd
def csv_to_df(path):
    return pd.read_csv(path, skiprows=1, sep='\t', comment='#')

What is the recommended pythonic way of adding type hints to this function?

If I ask python for the type of a DataFrame it returns pandas.core.frame.DataFrame. The following won't work though, as it'll tell me that pandas is not defined.

 def csv_to_df(path: str) -> pandas.core.frame.DataFrame:
     return pd.read_csv(path, skiprows=1, sep='\t', comment='#')

回答1:

Why not just use pd.DataFrame?

import pandas as pd
def csv_to_df(path: str) -> pd.DataFrame:
    return pd.read_csv(path, skiprows=1, sep='\t', comment='#')

Result is the same:

> help(csv_to_df)
Help on function csv_to_df in module __main__:
csv_to_df(path:str) -> pandas.core.frame.DataFrame

回答2:

I'm currently doing the following:

from typing import TypeVar
PandasDataFrame = TypeVar('pandas.core.frame.DataFrame')
def csv_to_df(path: str) -> PandasDataFrame:
    return pd.read_csv(path, skiprows=1, sep='\t', comment='#')

Which gives:

> help(csv_to_df)
Help on function csv_to_df in module __main__:

csv_to_df(path:str) -> ~pandas.core.frame.DataFrame

Don't know how pythonic that is, but it's understandable enough as a type hint, I find.

来源：https://stackoverflow.com/questions/43890844/pythonic-type-hints-with-pandas