\documentclass[12pt]{article}

\title{Python: Data Structures}

\author{FOSSEE}

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\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}