\documentclass[12pt]{article}


\title{Python: Data Structures}
\author{FOSSEE}
\usepackage{listings}
\lstset{language=Python,
    basicstyle=\ttfamily,
commentstyle=\itshape\bfseries, 
showstringspaces=false
}
\newcommand{\typ}[1]{\lstinline{#1}}
\usepackage[english]{babel}
\usepackage[latin1]{inputenc}
\usepackage{times}
\usepackage[T1]{fontenc}
\usepackage{ae,aecompl}
\usepackage{mathpazo,courier,euler}
\usepackage[scaled=.95]{helvet}

\begin{document}
\date{}
\vspace{-1in}
\begin{center}
\LARGE{Python Development}\\
\large{FOSSEE}
\end{center}
\section{Module}
Packages like \typ{scipy}, \typ{pylab} etc we used for functions like \typ{plot}, \typ{linspace} are \textbf{Modules}. They are Python script, which have various functions and objects, which can be imported and reused. 
\begin{lstlisting}
def gcd(a, b):
  if a % b == 0: 
    return b
  return gcd(b, a%b)

print gcd(15, 65)
print gcd(16, 76)
\end{lstlisting}
Save above mentioned python script with name 'gcd.py'. Now we can \typ{import} \typ{gcd} function. For example, in same directory create 'lcm.py' with following content:
\begin{lstlisting}
from gcd import gcd    

def lcm(a, b):
  return (a * b) / gcd(a, b)
    
print lcm(14, 56)
\end{lstlisting}
Here since both gcd.py and lcm.py are in same directory, import statement imports \typ{gcd} function from gcd.py.\\
When you try to run lcm.py it prints three results, two from gcd.py and third from lcm.py.
\begin{lstlisting}
$ python lcm.py
5
4
56
\end{lstlisting} %$
\newpage
We have print statements to make sure \typ{gcd} and \typ{lcm} are working properly. So to suppress output of \typ{gcd} module when imported in lcm.py we use \typ{'__main__'} \
\begin{lstlisting}
def gcd(a, b):
  if a % b == 0: 
    return b
  return gcd(b, a%b)
if __name__ == '__main__':
  print gcd(15, 65)
  print gcd(16, 76)
\end{lstlisting}
\typ{__main__()} helps to create standalone scripts. Code inside it is only executed when we run gcd.py. Hence
\begin{lstlisting}
$ python gcd.py
5
4
$ python lcm.py 
56
\end{lstlisting}
\end{document}