Object Oriented Programming With Python (part 1) - Self-Involved (
Page 5 of 6 )
You'll have noticed, in the
examples above, a curious little thingummy called "self". And you're probably
wondering what exactly it has to do with anything.
The "self" variable
has a lot to do with the way class methods work in Python. When a class method
is called, it requires to be passed a reference to the instance that is calling
it. This reference is passed as the first argument to the method, and is
represented by the "self" variable.
class veryBigSnake:
# some useful methods
def set_snake_name(self, name):
self.name = name
An example of this can be seen in the set_snake_name()
function above. When an instance of the class calls this method, a reference to
the instance is automatically passed to the method, together with the additional
"name" parameter. This reference is then used to update the "name" variable
belonging to that specific instance of the class.
Here's an example of
how this works:
>>> alpha = veryBigSnake()
>>> alpha.set_snake_name("Peter Python")
>>> alpha.name
'Peter Python'
>>>
Note that when you call a class method from an instance, you
do not need to explicitly pass this reference to the method - Python takes care
of this for you automatically.
With that in mind, consider this:
>>> alpha = test.veryBigSnake()
>>> veryBigSnake.set_snake_name(alpha, "Peter Python")
>>> alpha.name
'Peter Python'
>>>
In this case, I'm calling the class method directly (not via
an instance), but passing it a reference to the instance in the method call -
which makes this snippet equivalent to the one above it.
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