What is (self) in the python code? (OOP question)

Question

class MyController(BaseController):

    def index(self):
        # Return a rendered template
        #return render('/test.mako')
        # or, return a response
        return ''

Why does the function "index" have "self"?

I got this code from Pylons controller

Answer 1

It's a member function (a function that's part of a class), so when it's called, the object it was called on is automatically passed as the first argument.

For example:

c = MyController()
c.index()

would call index with self equal to c. self is the standard name, but you can call it anything you want

Answer 2

Many languages, like C++ and Java, have an implicit pointer inside member functions. In those languages, it is "this". Python, on the other hand, requires an EXPLICIT name to be given to that pointer. By convention, it is "self", although you could actually put anything you like in there as long as it is a valid identifier.

Answer 3

Whenever a method in an object is called, the first parameter passed into that method is the object itself. If you do not define the first parameter as being the object you are using, you will get a TypeError exception.