:orphan:

.. _notes_session09:

####################
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:

https://www.geeksforgeeks.org/underscore-_-python/

http://igorsobreira.com/2010/09/16/difference-between-one-underline-and-two-underlines-in-python.html


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.

.. code-block:: python

    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:


.. code-block:: python

    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``

https://github.com/UWPCE-PythonCert-ClassRepos/Wi2018-Classroom/blob/master/solutions/Session08/circle.py#L26

(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``


Object Oriented Mailroom
------------------------

One more time!

Yes, it's time to make mailroom Object oriented:

:ref:`exercise_mailroom_oo`