In Python, None is frequently used to represent the absence of a value -- a placeholder to define a null (empty) variable, object, or argument.

If you've heard about or used a NULL or nil type in another programming language, then this usage of None in Python will be familiar to you. None helps you to declare variables or function arguments that you don't yet have values for. These can then be re-assigned to specific values later as needed.

a = None
print(a)
#=> None
type(a)
#=> <class 'NoneType'>

# Adding a Default Argument with `None`
def add_to_todos(new_task, todo_list=None):
  if todo_list is None:
    todo_list = []
    todo_list.append(new_task)
  return todo_list

None will evaluate to False when used in a conditional check, so it is useful for validating the "presence of" or "absence of" a value - any value -- a pattern frequently used when a function or process might hand back an error object or message.

a = None
if a: #=> a will be evaluated to False when its used in a conditional check.
    print("This will not be printed")