Core Python Programming (2nd Edition)

11.2. Calling Functions
11.2.1. Function Operator
Functions are called using the same pair of parentheses that you are used to. In fact, some consider
( () ) to be a two-character operator, the function operator. As you are probably aware, any input
parameters or arguments must be placed between these calling parentheses. Parentheses are also used
as part of function declarations to define those arguments. Although we have yet to formally study
classes and object-oriented programming, you will discover that the function operator is also used in
Python for class instantiation.
11.2.2. Keyword Arguments
The concept of keyword arguments applies only to function invocation. The idea here is for the caller to
identify the arguments by parameter name in a function call. This specification allows for arguments to
be missing or out-of-order because the interpreter is able to use the provided keywords to match values
to parameters.
For a simple example, imagine a function foo(), which has the following pseudocode definition:
def foo(x):
foo_suite # presumably does some processing with 'x'
Standard calls to foo(): foo(42) foo('bar') foo(y)
Keyword calls to foo(): foo(x=42) foo(x='bar') foo(x=y)
For a more realistic example, let us assume you have a function called net_conn() and you know that it
takes two parameters, say, host and port:
def net_conn(host, port):
net_conn_suite
Naturally, we can call the function, giving the proper arguments in the correct positional order in which
they were declared:
net_conn('kappa', 8080)
The host parameter gets the string 'kappa' and port gets integer 8080. Keyword arguments allow out-oforder
parameters, but you must provide the name of the parameter as a "keyword" to have your
arguments match up to their corresponding argument names, as in the following:
net_conn(port=8080, host='chino')