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+\section{Functions}
+
+\begin{frame}[fragile]
+  \frametitle{Abstracting}
+  \begin{itemize}
+  \item Reduce duplication of code
+  \item Fewer lines of code and hence lesser scope for bugs
+  \item Re-usability of code, that's already been written
+  \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 Let's write a Python function, equivalent to this
+  \end{itemize}
+  \begin{lstlisting}
+    def f(x):
+        return x*x
+
+    f(1)
+    f(2)
+  \end{lstlisting}
+  \begin{itemize}
+  \item \texttt{def} is a keyword  
+  \item \texttt{f} is the name of the function 
+  \item \texttt{x} the parameter of the function
+  \item \texttt{return} is a keyword; specifies what should be
+    returned
+  \end{itemize}
+\end{frame}
+
+\begin{frame}[fragile]
+  \frametitle{Defining functions \ldots}
+  \begin{lstlisting}
+    def greet():
+        print "Hello World!"
+
+    greet()
+  \end{lstlisting}
+  \begin{itemize}
+  \item \texttt{greet} is a function that takes no arguments
+  \item Also, it is not returning anything explicitly
+  \item But implicitly, Python returns \texttt{None}
+  \end{itemize}
+  \begin{lstlisting}
+    def avg(a, b):
+        return (a + b)/2
+        
+    avg(12, 10)
+  \end{lstlisting}
+\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):
+        """ avg takes two numbers as input 
+        and returns their average"""
+
+        return (a + b)/2
+        
+    avg?
+    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 a 
+        circle given, the radius r"""
+
+        pi = 3.14
+        area = pi * r * r
+        perimeter = 2 * pi * r
+        return area, perimeter
+
+    circle(4)
+    a, p = circle(6)
+    print a
+    print p
+  \end{lstlisting}
+  \begin{itemize}
+  \item Any number of values can be returned
+  \end{itemize}
+\end{frame}
+
+\begin{frame}[fragile]
+  \frametitle{What? -- 1}
+  \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? -- 2}
+  \begin{lstlisting}
+    def what( n ):
+        i = 1
+        while i * i < n:
+            i += 1
+        return i * i == n, i
+  \end{lstlisting}
+\end{frame}
+
+\subsection*{Default \& Keyword Arguments}
+
+\begin{frame}[fragile]
+  \frametitle{Default arguments}
+  \begin{lstlisting}
+    round(2.484)
+    round(2.484, 2)
+
+    s.split() # split on spaces
+    s.split(';') # split on ';'
+
+    range(10) # returns numbers from 0 to 9
+    range(1, 10) # returns numbers from 1 to 9
+    range(1, 10, 2) # returns odd numbers from 1 to 9
+  \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+  \frametitle{Default arguments \ldots}
+  \begin{lstlisting}
+    def welcome(greet, name="World"):
+        print greet, name
+
+    welcome("Hi", "Guido")
+    welcome("Hello")
+  \end{lstlisting}
+  \begin{itemize}
+  \item Arguments with default values, should be placed at the end
+  \item The following definition is \alert{WRONG}
+  \end{itemize}
+  \begin{lstlisting}
+    def welcome(name="World", greet):
+        print greet, name
+  \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+  \frametitle{Keyword Arguments}
+  \begin{lstlisting}
+    def welcome(greet, name="World"):
+        print greet, name
+
+    welcome("Hello", "James")
+
+    welcome("Hi", name="Guido")
+
+    welcome(name="Guido", greet="Hey")
+
+    welcome(name="Guido", "Hey")
+  \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+  \frametitle{Built-in functions}
+  \begin{itemize}
+  \item Variety of built-in functions are available
+  \item \texttt{abs, any, all, len, max, min}
+  \item \texttt{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}
+    def change(q):
+        q = 10
+        print q
+
+    change(1)
+    print q
+  \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+  \frametitle{Variables inside function are local}
+  \begin{lstlisting}
+    n = 5
+    def change():
+        n = 10
+        print n
+    change()
+    print n
+  \end{lstlisting}
+  \begin{itemize}
+  \item Use the \texttt{global} statement to assign to global variables
+  \end{itemize}
+  \begin{lstlisting}
+    def change():
+        global n
+        n = 10
+        print n
+    change()
+    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}
+    name = ['Mr.', 'Steve', 'Gosling']
+    def change_name():
+        name[0] = 'Dr.'
+    change_name()
+    print name
+  \end{lstlisting}
+\end{frame}
+
+\begin{frame}[fragile]
+  \frametitle{Passing Arguments \ldots}
+  \begin{lstlisting}
+    n = 5
+    def change(n):
+        n = 10
+        print "n = %s inside change " %n
+    change(n)
+    print n
+  \end{lstlisting}
+  
+  \begin{lstlisting}
+    name = ['Mr.', 'Steve', 'Gosling']
+    def change_name(n):
+        n[0] = 'Dr.'
+        print "n = %s inside change_name" %n
+    change_name(n)
+    print name
+  \end{lstlisting}
+\end{frame}