Is it better to declare a variable in python: = None, or = str(), or = ""?

Question

Is it better to declare a variable in python as None if you need to assign it later inside a different local area? I could not find the best practice on this:

1. if it is just going to be one string/int/boolean?
2. if it is going to be a list/tuple/dictionary?

Appreciate your advice!

def get_executed_list(list_of_strings):
    """list_of_strings is a list"""

    updated_list = None

    for single_string in list_of_strings:
        single_string += "-executed"
        updated_list.append(single_string)

    return updated_list

OR

def get_executed_list(list_of_strings):
    """list_of_strings is a list"""
    
    updated_list = []
    
    for single_string in list_of_strings:
        single_string += "-executed"
        updated_list.append(single_string)
    
    return updated_list

OR

def get_executed_list(list_of_strings):
    """list_of_strings is a list"""
    
    updated_list = ""
    
    for single_string in list_of_strings:
        single_string += "-executed"
        updated_list.append(single_string)
    
    return updated_list

Answer 1

As pointed out, only your second example actually works.

As for the question itself, I would only initialise a value to None, for then to later reinitialise it to the intended data type, if you actually need to distinguish between the two states.

An example use case for this is a class that is intended to hold data read from an external source like a file. Say a text file of name/value pairs. Since the None type in Python has an undefined value, it can be distinguished from for instance 0, "" or [] when these can represent valid value entries in your file. You can then check if you received your data and it was empty, or it was never seen at all.