*arg, **arg

参数列表中，*args 被解释为列表，**args 被解释为字典：
4.7.3 Arbitrary Argument Lists
Finally, the least frequently used option is to specify that a
function can be called with an arbitrary number of
arguments. These arguments will be wrapped up in a tuple. Before
the variable number of arguments, zero or more normal arguments
may occur.
def fprintf(file, format, *args):
    file.write(format % args)
4.7.4 Unpacking Argument Lists
The reverse situation occurs when the arguments are already in a
list or tuple but need to be unpacked for a function call
requiring separate positional arguments. For instance, the
built-in range() function expects separate start and stop
arguments. If they are not available separately, write the
function call with the *-operator to unpack the arguments out of
a list or tuple:
>>> range(3, 6)             # normal call with separate arguments
[3, 4, 5]
>>> args = [3, 6]
>>> range(*args)            # call with arguments unpacked from a list
[3, 4, 5]