Bare asterisk in function arguments?

Question

What does a bare asterisk in the arguments of a function do?

When I looked at the pickle module, I see this:

pickle.dump(obj, file, protocol=None, *,         


        

Answer 1

While the original answer answers the question completely, just adding a bit of related information. The behaviour for the single asterisk derives from PEP-3102. Quoting the related section:

The second syntactical change is to allow the argument name to
be omitted for a varargs argument. The meaning of this is to
allow for keyword-only arguments for functions that would not
otherwise take a varargs argument:

    def compare(a, b, *, key=None):
        ...

In simple english, it means that to pass the value for key, you will need to explicitly pass it as key="value".