A call calls a callable object (e.g., a function) with a possibly empty series of arguments:
call: primary "(" [argument_list [","]] ")" argument_list: positional_arguments ["," keyword_arguments] | keyword_arguments positional_arguments: expression ("," expression)* keyword_arguments: keyword_item ("," keyword_item)* keyword_item: identifier "=" expression
A trailing comma may be present after an argument list but does not affect the semantics.
The primary must evaluate to a callable object (user-defined
functions, built-in functions, methods of built-in objects, class
objects, methods of class instances, and certain class instances
themselves are callable; extensions may define additional callable
object types). All argument expressions are evaluated before the call
is attempted. Please refer to section
If keyword arguments are present, they are first converted to
positional arguments, as follows. First, a list of unfilled slots is
created for the formal parameters. If there are N positional
arguments, they are placed in the first N slots. Next, for each
keyword argument, the identifier is used to determine the
corresponding slot (if the identifier is the same as the first formal
parameter name, the first slot is used, and so on). If the slot is
already filled, a TypeError exception is raised.
Otherwise, the value of the argument is placed in the slot, filling it
(even if the expression is
None, it fills the slot). When all
arguments have been processed, the slots that are still unfilled are
filled with the corresponding default value from the function
definition. (Default values are calculated, once, when the function
is defined; thus, a mutable object such as a list or dictionary used
as default value will be shared by all calls that don't specify an
argument value for the corresponding slot; this should usually be
avoided.) If there are any unfilled slots for which no default value
is specified, a TypeError exception is raised. Otherwise,
the list of filled slots is used as the argument list for the call.
If there are more positional arguments than there are formal parameter slots, a TypeError exception is raised, unless a formal parameter using the syntax "*identifier" is present; in this case, that formal parameter receives a tuple containing the excess positional arguments (or an empty tuple if there were no excess positional arguments).
If any keyword argument does not correspond to a formal parameter name, a TypeError exception is raised, unless a formal parameter using the syntax "**identifier" is present; in this case, that formal parameter receives a dictionary containing the excess keyword arguments (using the keywords as keys and the argument values as corresponding values), or a (new) empty dictionary if there were no excess keyword arguments.
Formal parameters using the syntax "*identifier" or "**identifier" cannot be used as positional argument slots or as keyword argument names. Formal parameters using the syntax "(sublist)" cannot be used as keyword argument names; the outermost sublist corresponds to a single unnamed argument slot, and the argument value is assigned to the sublist using the usual tuple assignment rules after all other parameter processing is done.
A call always returns some value, possibly
None, unless it
raises an exception. How this value is computed depends on the type
of the callable object.
If it is--