What are some examples of mutable default parameters in Python?

Can you explain mutable default parameters in Python with examples?

Sure! In Python, mutable default parameters can lead to unexpected behavior. For example, if you use a list as a default parameter, it can retain changes across function calls.

Can you show me a code example of that?

Absolutely! Here's a simple example:

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

print(append_to_list(1))  # Output: [1]
print(append_to_list(2))  # Output: [1, 2]

In this case, the list my_list retains its state between calls.

What should I do to avoid this issue?

To avoid this issue, you can use None as the default value and create a new list 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

This way, a new list is created for each function call.