What are mutable and immutable default arguments in Python?

Can you explain the difference between mutable and immutable default arguments in Python?

Sure! In Python, mutable default arguments are objects that can be changed, like lists or dictionaries, while immutable default arguments, like integers or strings, cannot be changed once created.

Can you give me an example of how this works in a function?

Absolutely! If you define a function with a list as a default argument, modifying that list will affect future calls to the function. For example:

def append_to_list(value, my_list=[]):
    my_list.append(value)
    return my_list

Calling append_to_list(1) will return [1], but calling it again with append_to_list(2) will return [1, 2].

What happens if I use an immutable type like a string as a default argument?

If you use an immutable type like a string, it won't change between function calls. For example:

def greet(name='World'):
    return f'Hello, {name}!'

Calling greet() will always return 'Hello, World!'. Changing the default argument in one call won't affect others.

Are there any best practices for using default arguments in Python?

Yes! It's generally recommended to use None as a default value and then initialize mutable objects inside the function. This avoids unexpected behavior. For example:

def safe_append(value, my_list=None):
    if my_list is None:
        my_list = []
    my_list.append(value)
    return my_list