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\documentclass[14pt,compress,aspectratio=169]{beamer}
\input{macros.tex}
\title[OOP Inheritance]{Advanced Python}
\subtitle{Object Oriented Programming: Inheritance}
\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 a new \lstinline{Talk} class
\item Puts together data and methods
\item Can make instances of the class
\item Each instance has its own data
\item Objects encapsulate data and behavior
\end{itemize}
\end{frame}
\begin{frame}[fragile, plain]
\frametitle{Recap: the Talk class}
\vspace*{-0.1in}
\begin{lstlisting}
class Talk:
"""A class for the Talks."""
def __init__(self, speaker, title, tags):
self.speaker = speaker
self.title = title
self.tags = tags
def get_speaker_firstname(self):
return self.speaker.split()[0]
def get_tags(self):
return self.tags.split(',')
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Instantiating a class to create objects}
\begin{lstlisting}
In []: bdfl = Talk('Guido van Rossum',
...: 'The History of Python',
...: 'python,history,C,advanced')
In []: bdfl.get_tags()
In []: bdfl.get_speaker_firstname()
In []: bdfl.tags
In []: type(bdfl)
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Classes: the big picture}
\begin{itemize}
\item Lets you create new data types
\item Class is a template for an object belonging to that class
\item Instantiating a class creates an instance (an object)
\item An instance encapsulates the state (data) and behavior
(methods)
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Objects and Methods}
\begin{itemize}
\item Objects group data with functions
\item Everything in Python is an object
\item Strings, lists, functions and even modules
\end{itemize}
\begin{lstlisting}
s = "Hello World"
s.lower()
l = [1, 2, 3, 4, 5]
l.append(6)
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Classes}
\begin{lstlisting}
In []: s = "Hello World"
In []: type(s)
\end{lstlisting}
\begin{itemize}
\item A new string, comes along with methods
\item A template or a blue-print, where these definitions lie
\item This blue print for building objects is called a
\lstinline{class}
\item \lstinline{s} is an object of the \lstinline{str} class
\item An object is an ``instance'' of a class
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Classes: inheritance}
\begin{itemize}
\item Allows you to define an inheritance hierarchy
\begin{itemize}
\item ``A Honda car \alert{is a} car.''
\item ``A car \alert{is an} automobile.''
\item ``A Python \alert{is a} reptile.''
\end{itemize}
\item All data/behavior of a car should be there in a ``Honda'' car
\item All data/behavior associated with a reptile ought to inhere in a snake
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Inheritance}
\vspace*{-0.1in}
\begin{itemize}
\item Suppose, we wish to write a \lstinline{Tutorial} class
\item It's almost same as \lstinline{Talk} except for minor differences
\item We can ``inherit'' from \lstinline{Talk}
\end{itemize}
\pause
\begin{lstlisting}
class Tutorial(Talk):
"""A class for the tutorials."""
def __init__(self, speaker, title, tags,
needs_computer=True):
super().__init__(speaker, title, tags)
self.needs_computer = needs_computer
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Inheritance}
\vspace*{-0.1in}
\begin{itemize}
\item Modified \lstinline{__init__} method
\item Inherits: \lstinline{get_tags} and
\lstinline{get_speaker_firstname}
\end{itemize}
\begin{lstlisting}
tut = Tutorial('Travis Oliphant',
'Numpy Basics',
'numpy,python,beginner')
tut.get_speaker_firstname()
tut.needs_computer
\end{lstlisting}
\end{frame}
\begin{frame}
\frametitle{Some points}
\begin{itemize}
\item \lstinline{Tutorial} is a subclass (or child) of \lstinline{Talk}
\item \lstinline{Talk} is the base class (or parent class)
\item Only the \lstinline{__init__} has been changed
\item This is called overriding
\item \lstinline{super} ensures that the parent class is called
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Exercise: try this}
\begin{lstlisting}
class Tutorial(Talk):
def __init__(self, speaker, title, tags,
needs_computer=True):
self.needs_computer = needs_computer
In []: t = Tutorial('G v R', 'Python', 'py,tut')
In []: t.needs_computer
In []: t.speaker
In []: t.get_speaker_firstname())
\end{lstlisting}
\end{frame}
\begin{frame}
\frametitle{Inheritance}
\begin{itemize}
\item A \lstinline{Tutorial} is a \lstinline{Talk}
\item A \lstinline{Talk} is not a \lstinline{Tutorial}
\item The sentence above should make sense!
\item A \lstinline{Cat} is an \lstinline{Animal}
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{Incorrect inheritance}
\begin{itemize}
\item A \lstinline{Talk} is a \lstinline{Speaker} or
\item A \lstinline{Speaker} is a \lstinline{Room}
\item Something is wrong in your OO design!
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Summary}
\begin{itemize}
\item Inheritance
\item The importance of making sense
\item The \lstinline{super} function
\end{itemize}
\end{frame}
\end{document}
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