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\documentclass[14pt,compress,aspectratio=169]{beamer}
\input{macros.tex}
\title[OOP containership]{Advanced Python}
\subtitle{Object Oriented Programming: containership }
\author[FOSSEE] {The FOSSEE Group}
\institute[IIT Bombay] {Department of Aerospace Engineering\\IIT Bombay}
\date[] {Mumbai, India}
\begin{document}
\begin{frame}
\titlepage
\end{frame}
\begin{frame}
\frametitle{Recap}
\begin{itemize}
\item Created \lstinline{Talk} and \lstinline{Tutorial} classes
\item Know how to create objects: instantiation of a class
\vspace*{0.5in}
\item Let us create a conference!
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Conference class}
\vspace*{-0.1in}
\begin{lstlisting}
class Conference:
def __init__(self, talks=None):
if talks is None:
talks = []
self.talks = talks
def add_talk(self, talk):
self.talks.append(talk)
def schedule(self):
for talk in self.talks:
print(talk.speaker, talk.title)
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Using this}
\begin{lstlisting}
In []: c = Conference()
In []: t = Talk('Guido', 'Python4', 'py,core')
In []: c.add_talk(t)
In []: c.schedule()
\end{lstlisting}
\begin{itemize}
\item Easy to read
\item Nicely split up
\item Reflects the real world
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{But why not this?}
\begin{lstlisting}
class Conference:
def __init__(self, talks=[]):
self.talks = talks
\end{lstlisting}
\begin{itemize}
\item Easier
\item Less code
\item Let's try it!
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Gotcha!}
\begin{lstlisting}
In []: c1 = Conference()
In []: c1.add_talk(1)
In []: c1.talks
In []: c2 = Conference()
In []: c2.talks
\end{lstlisting}
\begin{itemize}
\item What is going on?
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{Beware of mutable default arguments!}
\begin{itemize}
\item Default arguments are evaluated once
\item When the method/function is defined
\item So, if the object is mutable we have a problem
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Which is why we have this}
\begin{lstlisting}
class Conference:
def __init__(self, talks=None):
if talks is None:
talks = []
self.talks = talks
\end{lstlisting}
\end{frame}
\begin{frame}
\frametitle{Containership}
\begin{itemize}
\item \lstinline{Conference} class manages all the talks
\item It contains the talks and tutorials
\item Allows us to build complexity by \alert{composition}
\item Hierarchical organization
\item Allows us to mirror the real objects in code
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{Some more examples}
\begin{itemize}
\item OOP for a \lstinline{Company}
\item OOP for a \lstinline{Bank}
\item OOP for a \lstinline{School} or \lstinline{College}
\item OOP for a cell phone, computer, ...
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{Design guidelines}
\begin{itemize}
\item Important to make sense
\item Should be easy to explain the relationships and responsibilities of
each class
\item Inheritance should ``read'' correctly and make sense
\item No object should be too responsible
\item Functionality should be suitably delegated
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{Summary}
\begin{itemize}
\item Creating a more complex class
\item Containing other objects
\item Issue with mutable default arguments
\item Important design guidelines
\end{itemize}
\end{frame}
\begin{frame}[plain, fragile]
\frametitle{Exercise: Create a Zoo}
\begin{block}{}
Create a \py{Zoo} class which allows someone to add any number of animals.
This means it should work for \py{Animal, Mammal, Human} objects. It
should have a single \py{greet} method which calls the greet method of all
of the animals it has and prints that:
\end{block}
\begin{lstlisting}
In []: b = Animal('crow')
In []: m = Mammal('dog', legs=4)
In []: h = Human('Abhinav')
In []: z = Zoo(b, m, h)
In []: z.greet()
crow says greet
dog says greet
Abhinav says hello
\end{lstlisting}
\end{frame}
\begin{frame}[plain, fragile]
\frametitle{Solution}
\begin{lstlisting}
class Zoo:
def __init__(self, *animals):
self.animals = list(animals)
def greet(self):
for animal in self.animals:
print(animal.greet())
\end{lstlisting}
\end{frame}
\begin{frame}
\frametitle{Observations}
\begin{itemize}
\item Notice the abstraction of \py{Animal}
\item The \py{Zoo} will work with any object that has the \py{greet} method
\item That is, any \py{Animal}
\end{itemize}
\end{frame}
\end{document}
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