What are the best practices for using default arguments in Python?

What are the best practices for using default arguments in Python?

When using default arguments in Python, it's important to ensure that they are immutable types, like integers or strings, to avoid unexpected behavior.

Can you give an example of a mutable default argument issue?

Sure! If you use a list as a default argument, it can retain changes across function calls. For example:

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

Calling append_to_list(1) and then append_to_list(2) will result in [1, 2], not just [2].

How can I avoid this issue?

To avoid this, use None as the default value and initialize the mutable object inside the function:

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

Are there any other best practices I should know?

Yes! Always document your default arguments clearly, and consider whether the default value makes sense for all use cases of the function.