Beginning Python - From Novice to Professional

CHAPTER 6 ■ ABSTRACTION 119
WHAT IF I REALLY WANT TO?
If you really want to modify your parameter, you can use a little trick—wrap your value in a list:
>>> def inc(x): x[0] = x[0] + 1
...
>>> foo = [10]
>>> inc(foo)
>>> foo
[11]
Simply returning the new value is generally considered a cleaner solution.
Keyword Parameters and Defaults
The parameters we’ve been using until now are called positional parameters because their
positions are important—more important than their names, in fact. Consider the following
two functions:
def hello_1(greeting, name):
print '%s, %s!' % (greeting, name)
def hello_2(name, greeting):
print '%s, %s!' % (name, greeting)
They both do exactly the same thing, only with their parameter names reversed:
>>> hello_1('Hello', 'world')
Hello, world!
>>> hello_2('Hello', 'world')
Hello, world!
Sometimes (especially if you have many parameters) the order may be hard to remember.
To make things easier, you can supply the name of our parameter:
>>> hello_1(greeting='Hello', name='world')
Hello, world!
The order here doesn’t matter at all:
>>> hello_1(name='world', greeting='Hello')
Hello, world!
The names do, however (as you may have gathered):
>>> hello_2(greeting='Hello', name='world')
world, Hello!