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\documentclass[14pt,compress]{beamer}
\input{macros.tex}
\title[only kwargs]{Advanced Python}
\subtitle{Keyword-only args and closures}
\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{Overview}
\begin{itemize}
\item Only-keyword arguments
\item Higher-order functions
\item Closures
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Motivation}
\begin{itemize}
\item One can mix positional and keyword arguments
\end{itemize}
\begin{lstlisting}
In []: def f(a, b=2):
...: print(a, b)
In []: f(a=2, b=3)
2 3
In []: f(b=2, a=3)
3 2
In []: f(10, 20)
1 2
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Motivation}
\begin{itemize}
\item Function changes: positional arguments change in order or number
\item Accidentally passing an extra argument
\item Can we have purely keyword arguments?
\vspace*{0.5in}
\item Yes, in Python 3.x!
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Keyword-only arguments}
\begin{lstlisting}
In []: def f(a, *args, b=False):
...: print(a, args, b)
In []: f(1, 20)
1 (20,) False
In []: f(1, b=20)
1 () 20
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Keyword-only arguments}
\noindent Without any extra arguments:
\vspace*{0.25in}
\begin{lstlisting}
In []: def f(a, *, b=False):
...: print(a, b)
In []: f(1, 20)
TypeError: f() takes 1 positional arg...
\end{lstlisting}
\pause
\begin{lstlisting}
In []: f(1, b=20)
1 20
\end{lstlisting}
\end{frame}
\begin{frame}
\frametitle{Discussion}
\begin{itemize}
\item Solves the problem nicely
\item \typ{b}: can only be specified as keyword argument
\item Cannot be called as a positional argument
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Recap of higher-order functions}
\begin{lstlisting}
In []: def sqr(x):
...: return x*x
In []: def sum(func, n):
...: result = 0
...: for i in range(n):
...: result += func(n)
...: return result
In []: sum(sqr, 5)
Out[]: 125
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Recap of higher-order functions}
\begin{lstlisting}
def f():
def g(x):
return x+1
return g
In []: func = f()
In []: func(1)
In []: f()(1) # Also valid!
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Closures}
\begin{lstlisting}
def mul(x):
def g(y):
return y*x
return g
In []: twice = mul(2.0)
In []: twice(20)
Out[]: 40.0
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Closures ...}
\begin{lstlisting}
In []: twice = mul(3.0)
In []: twice(20)
Out[]: 60.0
\end{lstlisting}
\end{frame}
\begin{frame}
\frametitle{Discussion}
\begin{itemize}
\item \typ{g} uses \typ{x}
\item \typ{x} is different in each case
\item So \typ{twice, thrice} ``curry'' the passed \typ{x}
\item This function is called a closure
\item Encloses its local environment
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Higher-order functions}
\begin{itemize}
\item Functions that manipulate functions
\item Passing a function as an argument
\item A function that returns another function
\item A closure
\end{itemize}
\end{frame}
\end{document}
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