What are the common bugs associated with mutable default arguments in Python?

What are the common bugs associated with mutable default arguments in Python?

Mutable default arguments can lead to unexpected behavior, especially when they are modified. For example, if you use a list as a default argument and modify it, the default value is changed for all future calls.

Can you give me an example of this bug?

Sure! Here's a simple example:

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

If you call append_to_list(1) and then append_to_list(2), the second call will return [1, 2] instead of just [2].

How can I avoid this issue?

To avoid this issue, 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 common pitfalls with default arguments?

Yes, another common pitfall is using mutable objects in function signatures, which can lead to similar issues. Always be cautious with mutable defaults!