\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}