Python: define type of variable given into a function parameter-CodePudding

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'.)

CodePudding user response：

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