dictionary - Mutability of the **kwargs argument in Python

Question

Consider a case where I change the kwargs dict inside a method:

def print_arg(**kwargs):
    print kwargs.pop('key')

If I call the method pop_arg with a dictionary like this:

mydict = {'key':'value'}
print_arg(**mydict)

will mydict be changed by this call?

I am also interested in a more detailed explanation of the underlying method calling mechanism that lets mydict change or not.

Answer 1

No, mydict won't be changed. kwargs get unpacked into a new dictionary.

Consider the case where you have:

def print_arg(key=1,**kwargs):
    print key
    print kwargs

print_arg(**{'key':2,'foo':3,'bar':4})

In this case, it's obvious that kwargs is a different dict than you pass in because when it gets unpacked, it's missing the 'key' key.