argument of type 'nonetype' is not iterable

This error message typically occurs when you try to use an object that is NoneType as if it were iterable (meaning it can be looped over or indexed). NoneType is a special data type in Python that represents the absence of a value.

For example, if you try to iterate over a function that doesn't return anything (i.e. returns None), you'll get this error:

def my_function():
    print("Hello, world!")

result = my_function()
for letter in result:
    print(letter)

This will result in the error message "TypeError: 'NoneType' object is not iterable" because `my_function()` doesn't return anything, so `result` is None, and you can't loop over None.

To fix this error, make sure that any objects you're trying to iterate over or index are not None or check for NoneType before trying to use it as an iterable.