Write an extension to an existing python module

I want to write an extension to python's lib cairo. The plan is as follows:

cairo has a class named "Context" which is the canvas that the user draws geometric objects on it.

For example let cr be an instance of Context, then

cr.move_to(a,b)
cr.line_to(c,d)

will move the pen to (a,b) and then draw a line to (c,d).

I want to add another method to this lib, for example it's named "My_line_to": this function will draw an curve between (a,b) and (c,d)，not a straight line.( I still call it line_to() because it's geodesic line in hyperbolic geometry)

The usage is

cr.my_move_to(a,b)
cr.my_line_to(c,d)

I think I'd better make this extension into another file named "MyDrawer.py", but I have no idea how to implement this. I want to know what is the standard/elegant way to write one's extension of an existing module in this case?

Solution

Subclassing is your friend here. Just subclass the Context class and define an additional method.

from cairo import Context # or whatever is the path name
class ExtendedContext(Context): # subclass from ExtendedContext - inherits all methods and variables from Context
    def my_line_to(self, x, y):
        # define code here
    def my_move_to(self, x, y):
        # define code here

Then, when you want to use this new class, just import it and use it.