How to check list of strings parameter type from isinstance() method

Question

I want to try to handle the parameter type passed to the function by using isinstance() function. Basically, i want to check that whether passed list to the function contains only string or not. So, I wrote function as

def fun(parameter: list[str]):
    #want to check parameter type here

After getting the list, I want to ensure that it contains only strings. So, is there any way to check this from isinstance() function? Otherwise i have to make custom check by looping through the list.

Answer 1

This is kind of an odd, roundabout way of doing it, but here's how you could get away without using a loop. I prefer @OneCricketeer's answer in general though.

import numpy as np


def fun(parameter: list[str]):
    assert list(np.array(parameter, dtype=str)) == parameter
   ...

Passing dtype=str will cause any non-string items in parameter to be converted to strings in the resulting array, which you can then convert back to a list and compare to the original. The two will be equal only if all items were strings already.

You could also use np.array_equal() instead of wrapping the array in list() and comparing with ==, which would be more efficient if your parameter list is very large.

Answer 2

You can use 2 methods:
Method 1: Using the built-in function of python3 i.e isinstance().\

example:

def fun(parameter: list[str]):
 return isinstance(parameter, (list, str))

This will return the True or False. It will check parameter is list or string or a list of strings.

Method 2: create the custom function to check the type.

example:

def fun(parameter:list[str]):
     if type(parameter) == list:
            for i in parameter:
                 if type(i) != str:
                       return False
            return True
     return False

The logic behind the above code is simple it will check whether the parameter is list or not if a list will send False. If it is list then it will check the contains of the list are true or not. If they are true it simply returns True.