Beginning Python - From Novice to Professional

144 CHAPTER 7 ■ MORE ABSTRACTION
'Sir Lancelot'
This means that you have to worry about the contents of globalName when you use instances
(objects) of the class OpenObject. In fact, you have to make sure that nobody changes it:
>>> globalName = 'Sir Gumby'
>>> o.getName()
'Sir Gumby'
Things get even more problematic if you try to create more than one OpenObject because
they will all be messing with the same variable:
>>> o1 = OpenObject()
>>> o2 = OpenObject()
>>> o1.setName('Robin Hood')
>>> o2.getName()
'Robin Hood'
As you can see, setting the name of one automatically sets the name of the other. Not
exactly what you want.
Basically, you want to treat objects as abstract. When you call a method you don’t want to
worry about anything else, such as not disturbing global variables. So how can you “encapsulate”
the name within the object? No problem. You make it an attribute. Attributes are variables
that are a part of the object, just like methods; actually methods are almost like attributes
bound to functions. (You’ll see an important difference between methods and functions in the
section “Attributes, Functions, and Methods,” later in this chapter.)
If you rewrite the class to use an attribute instead of a global variable, and you rename it
ClosedObject, it works like this:
>>> c = ClosedObject()
>>> c.setName('Sir Lancelot')
>>> c.getName()
'Sir Lancelot'
So far, so good. But for all you know, this could still be stored in a global variable. Let’s
make another object:
>>> r = ClosedObject()
>>> r.setName('Sir Robin')
r.getName()
'Sir Robin'
Here we can see that the new object has its name set properly. Well, we expected that. But
what has happened to the first object now?
>>> c.getName()
'Sir Lancelot'