Notes for Session 09¶
A collection of notes to go over in class, to keep things organized.
Lightning Talks¶
James Takata
Katherine Marguerite Anderson
Matthew D Briggs
[Make sure you’ve got the right adapter….]
Issues that came up during the week.¶
Adding parameters to a subclass __init__¶
In general, when you override a method in a subclass, you want the method signature to be the same. That is – all the parameters should be the same.
However, sometimes, particularly with __init__, you may need a couple extra parameters. To keep things clean and extensible, you want to put the extra parameters at the beginning, before the super class’ parameters:
And this lets you use *args and **kwargs to pass along the usual ones.
class Base:
def __init__(self, par1, par2, par3=something, par4=something):
...
class Subclass(Base):
def __init__(self, newpar1, newpar2, *args, **kwargs):
self.newpar1 = newpar1
self.newpar2 = newpar2
super().__init__(*args, **kwarg)
Example: html_render Anchor tag:
class A(OneLineTag):
"""
anchor element
"""
tag = "a"
def __init__(self, link, *args, **kwargs):
kwargs['href'] = link
super().__init__(*args, **kwargs)
This becomes particularly important with super() and subclassing…
which we will get more into today.
Any other html_render questions?¶
New Topics¶
sorting¶
maybe it’s a good idea to add a sort_key method to your classes?
see IntroPython-2017/examples/Session09/sort_key.py
let’s try it on Circle….
classmethod¶
classmethod is really pretty simple to use, not much to talk about. But it can be a bit challenging to “get”.
The key point is that classmethods work for subclasses – like for alternate constructors.
Let’s look at that with my Circle solution:
IntroPython-2017/solutions/Session08/circle.py
(and answer any other questions about Circle, while we are at it)
multiple inheritance and super()¶
super() is a mixed bag –it’s actually a pretty complex topic, but can be pretty easy to use – at least in the easy cases.
To get the hang of multiple inheritance, mix-ins, and super(), we’ll play around with object canvas:
See: IntroPython-2017/examples/Session09/object_canvas.py