Notes for Session 09¶
A collection of notes to go over in class, to keep things organized.
Due Date/Time¶
All submissions’ due dates/times are now set to 6pm, Monday, 5/14/2018. Letter grading will start at that time with all the submissions made by that time. If you miss this deadline and haven’t achieved 80% of the total possible score, you’ll be given an I (incomplete) grade and a 2-week extension. We’ll notify you if we have to give you an I grade and ask you to follow up.
Lightning Talks¶
Anyone missed their chance?
Issues that came up during the week.¶
“private” attributes and dunders¶
_something vs __something vs __something__
Let’s talk about that… See the following articles:
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?¶
Lightning Talks¶
Anyone missed?
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… (or on Fraction ?)
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