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+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%Tutorial slides on Python.
+%
+% Author: FOSSEE
+% Copyright (c) 2017, FOSSEE, IIT Bombay
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\documentclass[14pt,compress]{beamer}
+\input{macros.tex}
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% Title page
+\title[Functions]{Python language: Functions}
+
+\author[FOSSEE Team] {The FOSSEE Group}
+
+\institute[IIT Bombay] {Department of Aerospace Engineering\\IIT Bombay}
+\date[] {Mumbai, India}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% DOCUMENT STARTS
+\begin{document}
+
+\begin{frame}
+ \titlepage
+\end{frame}
+
+\section{Functions}
+
+\begin{frame}[fragile]
+ \frametitle{Functions for abstraction}
+ \begin{itemize}
+ \item Reduce duplication of code
+ \item Fewer lines of code: lesser scope for bugs
+ \item Re-usability of code
+ \item Use functions written by others, without exactly knowing how
+ they do, what they are doing
+ \item \alert{Enter Functions!}
+ \end{itemize}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{Defining functions}
+ \begin{itemize}
+ \item Consider the function \texttt{f(x) = x\textasciicircum{}2}
+ \item In Python:
+ \end{itemize}
+ \begin{lstlisting}
+ In []: def f(x):
+ .....: return x*x
+ .....:
+ In []: f(1)
+ In []: f(1+2j)
+ \end{lstlisting}
+ \begin{itemize}
+ \item \typ{def} is a keyword
+ \item \typ{f} is the name of the function
+ \item \typ{x} the parameter of the function
+ \item \typ{return} is a keyword
+ \end{itemize}
+\end{frame}
+
+
+\begin{frame}[fragile]
+ \frametitle{Defining functions \ldots}
+ \begin{lstlisting}
+ In []: def greet():
+ .....: print("Hello World!")
+ .....:
+
+ In []: greet()
+ \end{lstlisting}
+ \begin{itemize}
+ \item \texttt{greet} is a function that takes no arguments
+ \item It returns nothing explicitly
+ \item Implicitly, Python returns \typ{None}
+ \item \typ{None} is also a built-in, immutable data type
+ \end{itemize}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{Defining functions \ldots}
+ \begin{lstlisting}
+ In []: def avg(a, b):
+ .....: return (a + b)/2
+ .....:
+
+ In []: avg(12, 10)
+\end{lstlisting}
+\begin{itemize}
+\item \typ{avg} takes two arguments
+\item Returns one value
+\end{itemize}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{Doc-strings}
+ \begin{itemize}
+ \item It's highly recommended that all functions have documentation
+ \item We write a doc-string along with the function definition
+ \end{itemize}
+ \begin{lstlisting}
+def avg(a, b):
+ """Returns the average of two
+ given numbers."""
+ return (a + b)/2
+
+In[]: avg?
+In[]: greet?
+ \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{Returning multiple values}
+ \begin{itemize}
+ \item Return area and perimeter of circle, given radius
+ \item Function needs to return two values
+ \end{itemize}
+ \begin{lstlisting}
+def circle(r):
+ """Returns area and perimeter of
+ circle given radius r"""
+ pi = 3.14
+ area = pi * r * r
+ perimeter = 2 * pi * r
+ return area, perimeter
+
+In []: circle(4)
+In []: a, p = circle(6)
+ \end{lstlisting}
+\end{frame}
+
+
+\subsection{Default \& Keyword Arguments}
+
+\begin{frame}[fragile]
+ \frametitle{Default arguments}
+ \begin{lstlisting}
+In []: round(2.484)
+In []: round(2.484, 2)
+
+In []: s.split() # split on spaces
+In []: s.split(';') # split on ';'
+
+In []: range(10)
+In []: range(1, 10)
+In []: range(1, 10, 2)
+ \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{Default arguments \ldots}
+ \begin{lstlisting}
+In []: def welcome(greet, name="World"):
+.....: print(greet, name)
+.....:
+
+In []: welcome("Hi", "Guido")
+In []: welcome("Hello")
+ \end{lstlisting}
+\end{frame}
+\begin{frame}[fragile]
+ \frametitle{Default arguments \ldots}
+ \begin{itemize}
+ \item Arguments with default values, should be placed at the end
+ \item The following definition is \alert{WRONG}
+ \end{itemize}
+ \begin{lstlisting}
+In []: def welcome(name="World", greet):
+.....: print(greet, name)
+.....:
+ \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile,plain]
+ \frametitle{Keyword Arguments}
+ \begin{lstlisting}
+In []: def welcome(greet, name="World"):
+.....: print(greet, name)
+.....:
+
+In []: welcome("Hello", "James")
+
+In []: welcome("Hi", name="Guido")
+
+In []: welcome(name="Guido",greet="Hey")
+
+In []: welcome(name="Guido", "Hey")
+\end{lstlisting}
+Cannot have non-keyword args after kwargs
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{Built-in functions}
+ \begin{itemize}
+ \item Variety of built-in functions are available
+ \item \typ{abs, any, all, len, max, min}
+ \item \typ{pow, range, sum, type}
+ \item Refer here:
+ \url{http://docs.python.org/library/functions.html}
+ \end{itemize}
+\end{frame}
+
+\subsection{Variable Scope}
+
+\begin{frame}[fragile]
+ \frametitle{Arguments are local}
+ \begin{lstlisting}
+ In []: def change(q):
+ .....: q = 10
+ .....: print(q)
+ .....:
+
+ In []: change(1)
+ In []: print(q)
+ \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{Variables inside function are local}
+ \begin{lstlisting}
+ In []: n = 5
+ In []: def change():
+ .....: n = 10
+ .....: print(n)
+ .....:
+ In []: change()
+ In []: print(n)
+ \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{If not defined, look in parent scope}
+ \begin{lstlisting}
+ In []: n = 5
+ In []: def scope():
+ .....: print(n)
+ .....:
+ In []: scope()
+\end{lstlisting}
+\begin{itemize}
+\item Note that \typ{n} was not defined in \typ{scope}
+\item It looked for the variable in previous scope
+\item See: \url{pythontutor.com}
+\end{itemize}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{\texttt{global}}
+ \begin{itemize}
+ \item Use the \texttt{global} statement to assign to global variables
+ \end{itemize}
+ \begin{lstlisting}
+ In[]: def change():
+ ....: global n
+ ....: n = 10
+ ....: print(n)
+ ....:
+ In[]: change()
+ In[]: print(n)
+ \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{Mutable variables}
+ \begin{itemize}
+ \item Behavior is different when assigning to a list element/slice
+ \item Python looks up for the name, from innermost scope outwards,
+ until the name is found
+ \end{itemize}
+ \begin{lstlisting}
+In []: name = ['Mr.', 'Steve','Gosling']
+In []: def change_name():
+.....: name[0] = 'Dr.'
+.....:
+In []: change_name()
+In []: print(name)
+ \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{Passing Arguments \ldots}
+ \begin{lstlisting}
+In []: n = 5
+In []: def change(n):
+.....: n = 10
+.....: print(n, "inside change")
+.....:
+In []: change(n)
+In []: print(n)
+ \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{Passing Arguments \ldots}
+\begin{lstlisting}
+In []: name = ['Mr.', 'Steve','Gosling']
+In []: def change_name(x):
+.....: x[0] = 'Dr.'
+.....: print(x, 'in change')
+.....:
+In []: change_name(name)
+In []: print(name)
+ \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{Passing Arguments \ldots}
+\begin{lstlisting}
+In []: name = ['Mr.', 'Steve','Gosling']
+In []: def change_name(x):
+.....: x = [1,2,3]
+.....: print(x, 'in change')
+.....:
+In []: change_name(name)
+In []: print(name)
+ \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{Passing Arguments \ldots}
+\begin{lstlisting}
+In []: name = ['Mr.', 'Steve','Gosling']
+In []: def change_name(x):
+.....: x[:] = [1,2,3]
+.....: print(x, 'in change')
+.....:
+In []: change_name(name)
+In []: print(name)
+ \end{lstlisting}
+\end{frame}
+
+
+\subsection{Examples}
+
+\begin{frame}[fragile]
+ \frametitle{Functions: example}
+ \begin{lstlisting}
+def signum( r ):
+ """returns 0 if r is zero
+ -1 if r is negative
+ +1 if r is positive"""
+ if r < 0:
+ return -1
+ elif r > 0:
+ return 1
+ else:
+ return 0
+ \end{lstlisting}
+ \emphbar{Note docstrings}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle {What does this function do?}
+ \begin{lstlisting}
+def what(n):
+ if n < 0: n = -n
+ while n > 0:
+ if n % 2 == 1:
+ return False
+ n /= 10
+ return True
+ \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{What does this function do?}
+\begin{lstlisting}
+def what(n):
+ i = 1
+ while i * i < n:
+ i += 1
+ return i * i == n, i
+ \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle {What does this function do?}
+ \begin{lstlisting}
+def what(x, n):
+ if n < 0:
+ n = -n
+ x = 1.0 / x
+
+ z = 1.0
+ while n > 0:
+ if n % 2 == 1:
+ z *= x
+ x *= x
+ n //= 2
+ return z
+ \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{Nested functions}
+ \begin{lstlisting}
+ def f(x):
+ def g(x):
+ return x+1
+ return g(x)**2
+ \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+ \frametitle{Nested functions: returning 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}
+ \frametitle{Summary}
+ \begin{itemize}
+ \item Defining functions
+ \item Taking either 0, or more arguments
+ \item Returning \typ{None} implicitly or any number of values
+ \item Default and keyword arguments
+ \item Variable scope, \typ{global}
+ \item Mutable and immutable arguments
+ \item Nested functions
+ \end{itemize}
+\end{frame}
+
+\end{document}
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