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%Tutorial slides on Python.
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% Author: FOSSEE
% Copyright (c) 2017, FOSSEE, IIT Bombay
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\title[Modules]{Python language: modules}
\author[FOSSEE Team] {The FOSSEE Group}
\institute[IIT Bombay] {Department of Aerospace Engineering\\IIT Bombay}
\date[] {Mumbai, India}
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% DOCUMENT STARTS
\begin{document}
\begin{frame}
\titlepage
\end{frame}
\section{Python modules}
\begin{frame}
\frametitle{Modules}
\begin{itemize}
\item Organize your code
\item Collect similar functionality
\item Functions, classes, constants, etc.
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{Modules}
\begin{itemize}
\item Define variables, functions and classes in a file with a
\texttt{.py} extension
\item This file becomes a module!
\item File name should be valid variable name
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{Modules \ldots}
\begin{itemize}
\item The \typ{import} keyword ``loads'' a module
\item One can also use:
\mbox{\typ{from module import name1, name2}}\\
where \typ{name1} etc. are names in the module, \typ{module}
\item \typ{from module import *} \ --- imports everything from module,
\alert{use only in interactive mode}
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Note on module file names}
\begin{itemize}
\item Should start with a letter or underscore
\item Can use \typ{\_} (underscore) and numbers
\item No \typ{.} allowed
\item No spaces or special characters
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Test}
\begin{itemize}
\item \typ{1\_script.py}
\item \typ{script\_1.py}
\item \typ{one11.py}
\item \typ{\_one11.py}
\item \typ{one script.py}
\item \typ{one,script;xxx.py}
\item \typ{one.two.py}
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Modules: example}
\begin{lstlisting}
# --- fib.py ---
some_var = 1
def fib(n):
"""Print Fibonacci series up to n.
"""
a, b = 0, 1
while b < n:
print(b, end=' ')
a, b = b, a+b
# EOF
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Modules: example}
\begin{lstlisting}
>>> import fib
>>> fib.fib(10)
1 1 2 3 5 8
>>> fib.some_var
1
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Python path}
\begin{itemize}
\item In IPython type the following
\end{itemize}
\begin{lstlisting}
import sys
sys.path
\end{lstlisting}
\begin{itemize}
\item List of locations where python searches for a module
\item \texttt{import sys} -- searches for file \texttt{sys.py} or
dir \texttt{sys} in all these locations
\item Modules can be in any one of the locations
\item Current working directory is one of the locations
\item Can also set \texttt{PYTHONPATH} env var
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Running a module}
\begin{itemize}
\item Let us say we want to run some code in \typ{fib.py} so we get:
\end{itemize}
\begin{lstlisting}
$ python fib.py
1 1 2 3 5 8
\end{lstlisting} %$
\end{frame}
\begin{frame}[fragile]
\frametitle{Modules: Running a module}
\begin{lstlisting}
# --- fib.py ---
some_var = 1
def fib(n):
"""Print Fibonacci series up to n.
"""
a, b = 0, 1
while b < n:
print(b, end=' ')
a, b = b, a+b
fib(10)
# EOF
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Modules: example}
\begin{lstlisting}
>>> import fib
1 1 2 3 5 8
\end{lstlisting}
\begin{itemize}
\item So the code is called even when we import the module
\item We do not want this!
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Using \texttt{\_\_name\_\_}}
\begin{lstlisting}
import fib
\end{lstlisting}
\begin{itemize}
\item The import is successful
\item But \typ{fib(10)}, gets run
\pause
\item Add it to the following \texttt{if} block
\end{itemize}
\begin{lstlisting}
if __name__ == "__main__":
fib(10)
\end{lstlisting}
\begin{itemize}
\item Now the script runs properly
\item As well as the import works; the code is not executed
\item \texttt{\_\_name\_\_} is local to every module and is equal
to \texttt{'\_\_main\_\_'} only when the file is run as a script.
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Modules: using \typ{\_\_name\_\_}}
\vspace*{-1ex}
\begin{lstlisting}
# --- fib.py ---
def fib(n):
"""Print Fibonacci series up to n.
"""
a, b = 0, 1
while b < n:
print(b, end=' ')
a, b = b, a+b
print(__name__)
if __name__ == '__main__':
fib(10)
# EOF
\end{lstlisting}
\end{frame}
\begin{frame}[fragile]
\frametitle{Modules: using \typ{\_\_name\_\_}}
\begin{lstlisting}
>>> import fib
\end{lstlisting}
Try this:
\begin{lstlisting}
$ python fib.py
\end{lstlisting} %$
\end{frame}
\begin{frame}[fragile]
\frametitle{Stand-alone scripts}
Consider a file \texttt{f.py}:
\footnotesize
\begin{lstlisting}
#!/usr/bin/env python
"""Module level documentation."""
# First line tells the shell that it should use Python
# to interpret the code in the file.
def f():
print "f"
# Check if we are running standalone or as module.
# When imported, __name__ will not be '__main__'
if __name__ == '__main__':
# This is not executed when f.py is imported.
f()
\end{lstlisting}
\end{frame}
\begin{frame}
\frametitle{Standard library}
\begin{itemize}
\item Operating system interface: \typ{os}, \typ{os.path}
\item System, Command line arguments: \typ{sys}
\item Regular expressions: \typ{re}
\item Math: \typ{math}, \typ{random}
\item Internet access: \typ{urllib}, \typ{smtplib}
\item Data compression: \typ{zlib}, \typ{gzip}, \typ{bz2},
\typ{zipfile}, and \typ{tarfile}
\item Unit testing: \typ{doctest} and \typ{unittest}
\item And a whole lot more!
\item Check out the Python Library reference:
\url{http://docs.python.org/lib/lib.html}
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Summary}
\begin{itemize}
\item Creating modules
\item Importing modules
\item Running modules as scripts
\item \texttt{\_\_name\_\_}
\end{itemize}
\end{frame}
\end{document}