Python：定义给定函数参数的变量类型

Question

I have a python function with a variable file. My problem is now, I want to work with the filename.

My problem now is, the type of variable is not known automatically inside of the function. What easy possibilities do I have to determine the variable to be a file?

   import pandas_datareader as web
   import pandas as pd
   import pickle


   def import_prices(file, start, end):
       tickers = pickle.load(file)
       main_df = pd.DataFrame()
       i = 0
       for ticker in tickers:
           df = web.DataReader(ticker, 'yahoo', start, end)
           df.rename(columns={"Adj Close": ticker}, inplace=True)
           df.drop(columns=["Open", "High", "Low",
                "Close", "Volume"], inplace=True)
           if main_df.empty:
               main_df = df
           else:
               main_df = main_df.join(df, how='outer')
           i = i + 1
           print(i)
       main_df.to_csv('Webscrapper/{}_prices.csv'.)

the filename without the stuff after the dot I want to insert into the brackets of

main_df.to_csv('Webscrapper/{}_prices.csv'.)

Answer 1

The file variable should contain a filename as I see in your code. You could check the following to be sure that the file contains a string value isinstance(file, str) .

You could also use more complex checks like isinstance(file, pd.DataFrame) or

from io import IOBase

isinstance(someobj, IOBase)

It would be better to use type hints in the function definition. I assume that start and end are ints but you could change this to match the right type.

def import_prices(file: str, start: int, end: int) -> None