How do I use default arguments correctly in Python?

How do I use default arguments correctly in Python?

In Python, you can define default arguments in a function by assigning a value to the parameter in the function definition. For example:

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

This way, if you call greet() without an argument, it will use 'Guest' as the default.

Can you give me an example of when to use default arguments?

Sure! Default arguments are useful when you want to provide a common value but still allow the user to override it. For instance:

def add(a, b=5):
    return a + b

Here, if you call add(3), it will return 8, but if you call add(3, 2), it will return 5.

What happens if I change the default argument value later?

If you change the default argument value in the function definition, it will affect all future calls to that function. However, if you have already called the function with the old default value, those calls will not change. For example:

def multiply(x, factor=2):
    return x * factor

If you later change factor to 3, existing calls using the old default will still use 2.

Are there any pitfalls I should be aware of?

Yes, one common pitfall is using mutable default arguments, like lists or dictionaries. If you modify the default argument, it will persist across function calls. For example:

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

This can lead to unexpected behavior. Instead, use None as a default and create a new list inside the function.