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\documentclass[14pt,compress,aspectratio=169]{beamer}
\usepackage{hyperref}
\input{macros.tex}
\title[OOP: multiple inheritance]{Advanced Python}
\subtitle{Object Oriented Programming: Multiple 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}[fragile]
\frametitle{Overview}
\begin{itemize}
\item Thus far, single inheritance
\end{itemize}
\begin{lstlisting}
class Animal:
def greet(self): ...
class Cat(Animal):
def greet(self): ...
class Dog(Animal):
def greet(self): ...
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Motivation}
\begin{itemize}
\item What if you wanted two parents?
\end{itemize}
\begin{lstlisting}
class Animal:
def eat(self): pass
\end{lstlisting}
\pause
\begin{lstlisting}
class Mammal(Animal):
def hair_color(self): pass
\end{lstlisting}
\pause
\begin{lstlisting}
class FlyingAnimal(Animal):
def fly(self): pass
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Motivation \ldots}
\begin{lstlisting}
class Bat(Mammal, FlyingAnimal):
pass
In []: b = Bat()
In []: b.eat(), b.hair_color(), b.fly()
\end{lstlisting}
\vspace*{0.25in}
\footnotesize{Example from \href{https://en.wikipedia.org/wiki/Virtual_inheritance}{Wikipedia}}
\end{frame}
\begin{frame}
\frametitle{Observations}
\begin{itemize}
\item \py{Mammal} is an \py{Animal}
\item \py{FlyingAnimal} is an \py{Animal}
\item \py{FlyingAnimal} is not a \py{Mammal}
\item \py{Bat} is a \py{Mammal} and a \py{FlyingAnimal}
\end{itemize}
\end{frame}
\begin{frame}[fragile, plain]
\frametitle{Multiple inheritance and super}
\small
\vspace*{-0.1in}
\begin{lstlisting}
class Base:
def __init__(self):
print('Base')
class A(Base):
def __init__(self):
print('A')
super().__init__()
class B(Base):
def __init__(self):
print('B')
super().__init__()
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Multiple inheritance and super}
\small
\begin{lstlisting}
class C(A, B):
def __init__(self):
print('C')
super().__init__()
In []: c = C()
C
A
B
Base
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Changing the order of parents}
\small
\begin{lstlisting}
class C1(B, A):
def __init__(self):
print('C')
super().__init__()
In []: c1 = C1()
C1
B
A
Base
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{\py{mro}: method resolution order}
\begin{itemize}
\item \py{mro} method shows order of calls
\item A method on the class object, not the instance
\end{itemize}
\begin{lstlisting}
In []: C.mro()
Out[]: [__main__.C, __main__.A, __main__.B,
__main__.Base, object]
In []: C1.mro()
Out[]: [__main__.C1, __main__.B, __main__.A,
__main__.Base, object]
\end{lstlisting}
\end{frame}
\begin{frame}[fragile, plain]
\frametitle{Another example}
\small
\vspace*{-0.1in}
\begin{lstlisting}
class A:
def __init__(self):
print('A')
class B:
def __init__(self):
print('B')
class C(A, B):
def __init__(self):
print('C')
super().__init__()
In []: c = C()
C
A
\end{lstlisting}
\end{frame}
\begin{frame}
\frametitle{Observations}
\begin{itemize}
\item \py{A} and \py{B} did not call \py{super}
\item \py{super} is what calls the parent \py{__init__}
\item The order of calls is determined by \py{mro}
\item This works for any method, not just \py{__init__}
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Question}
\begin{itemize}
\item What if \py{C} did not call \py{super}?
\end{itemize}
\begin{lstlisting}
class C(A, B):
def __init__(self):
print('C')
In []: c = C()
\end{lstlisting}
\end{frame}
\begin{frame}
\frametitle{Learning more}
\begin{itemize}
\item See: \url{docs.python.org/3.6/tutorial/classes.html}
\item See: \url{www.python.org/download/releases/2.3/mro/}
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{Summary}
\begin{itemize}
\item Multiple base classes
\item Important of \py{super}
\item \py{mro} determines order of calls
\end{itemize}
\end{frame}
\end{document}
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