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\documentclass[14pt,compress,aspectratio=169]{beamer}
\usepackage{hyperref}
\input{macros.tex}
\title[OOP: special methods]{Advanced Python}
\subtitle{Object Oriented Programming: special methods}
\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{Special methods}
\begin{itemize}
\item \py{__init__} is one such method
\item \py{__}, dunder, on both sides
\item Support operations on the object
\item Pretty string representations
\item Numerical data types supporting addition/ multiplication etc.
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Motivating example}
\begin{lstlisting}
class Value:
def __init__(self, x=0):
self.x = x
In []: a = Value()
In []: print(a)
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Motivation: \typ{str} and \typ{repr}}
\begin{lstlisting}
In []: import numpy as np
In []: x = np.array([1,2,3])
In []: print(x)
[1 2 3]
In []: str(x)
'[1 2 3]'
In []: repr(x)
'array([1, 2, 3])'
\end{lstlisting}
\begin{itemize}
\item \py{print} uses \py{str}
\item \py{repr} seems to show how to create the object
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{The \py{__str__} method}
\begin{lstlisting}
class Value:
def __init__(self, x=0):
self.x = x
def __str__(self):
return str(self.x)
In []: a = Value()
In []: print(a)
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{The \py{__repr__} method}
\begin{lstlisting}
class Value:
def __init__(self, x=0):
self.x = x
def __str__(self):
return str(self.x)
def __repr__(self):
return 'Value(%s)' % self.x
In []: a = Value()
In []: repr(a)
\end{lstlisting}
\end{frame}
\begin{frame}
\frametitle{Doing more}
\begin{itemize}
\item Have many more of these special methods
\item Explore later
\item See: \url{docs.python.org/reference/datamodel.html\#special-method-names}
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{Summary}
\begin{itemize}
\item Introduction to special methods
\item \py{__str__} and \py{__repr__}
\end{itemize}
\end{frame}
\begin{frame}[plain, fragile]
\frametitle{Exercise: \py{Point} class}
\begin{block}{}
Write a \py{Point} class with two attributes \py{x, y} with useful
\py{__str__, __repr__} methods as follows.
\end{block}
\begin{lstlisting}
In []: p = Point(1, 2)
In []: str(p)
'(1, 2)'
In []: repr(p)
'Point(1, 2)'
\end{lstlisting}
\end{frame}
\begin{frame}[plain, fragile]
\frametitle{Solution}
\begin{lstlisting}
class Point:
def __init__(self, x=0, y=0):
self.x = x
self.y = y
def __str__(self):
return '(%s, %s)' % (self.x, self.y)
def __repr__(self):
return 'Point' + self.__str__()
\end{lstlisting}
\end{frame}
\end{document}
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