%%%%%%%%%%%%python description starts
\section{Reading pushbutton status from Python}
\subsection{Reading the pushbutton status}
In this section, we discuss how to carry out the experiments of the
previous section from Python.  We will list the same two experiments,
in the same order.  The Shield has to be attached to the \arduino\ board
before doing these experiments and the \arduino\ needs to be connected to the computer 
with a USB cable, as shown in \figref{arduino}.
The reader should go through the instructions given in
\secref{sec:python-start} before getting started.

\begin{enumerate}
\item In the first experiment, we will read the pushbutton status. The code for this experiment is given in
  \pyref{py:push-100}. As explained earlier in \secref{sec:light-py}, we begin with 
  importing necessary modules followed by setting up the serial port. 
  Then, we read the input coming from digital pin 12 using the
  following command:
  \lstinputlisting[firstline=26,lastline=26]
  {\LocPushpycode/push-button-status.py} Note that the one leg of the pushbutton on
  the Shield is connected to digital pin 12 of \arduino\, 
  as given in \figref{fig:pushbuttonconn}. The read value is displayed (or printed) 
 by the following lines: 
   \lstinputlisting[firstline=25,lastline=28]
  {\LocPushpycode/push-button-status.py} where {\tt val} contains
  the pushbutton value acquired by the previous command. When the pushbutton is not pressed, {\tt val} will be ``0''. On the other hand,
  when the pushbutton is pressed, {\tt val} will be ``1''.
  To encourage the user to have a good hands-on, we run these commands in
  a {\tt for} loop for 20 iterations. The readers are encouraged to change the number 
  of iterations as per their requirements. While running this experiment, the readers must press
  and release the pushbutton and observe the values being printed on the
  Command Prompt (on Windows) or Terminal (on Linux), as the case maybe.


\item This experiment is an extension of the previous
  experiment. Here, we control the state of an LED as per the status
  of the pushbutton. In other words, digital output to an LED is
  decided by the digital input received from the pushbutton. The code
  for this experiment is given in \pyref{py:push-200}. After reading
  the pushbutton status, we turn the LED on if the pushbutton is
  pressed, otherwise we turn it off. The following lines,
  \lstinputlisting[firstline=28,lastline=31]
  {\LocPushpycode/led-push-button.py} control the LED state based on the status 
  of the pushbutton. While running this experiment, the readers must press and release the 
  pushbutton. Accordingly, they can observe whether the LED glows when the pushbutton is pressed.
\end{enumerate}

\subsection{Python Code}
\lstset{style=mystyle}
\label{sec:push-python-code}
\addtocontents{pyd}{\protect\addvspace{\codclr}}

\begin{pycode}
\pcaption{Read the status of the pushbutton and display it on the
  Command Prompt or the Terminal}{Read the status of the pushbutton and display it on
  Command Prompt or the Terminal.  Available at
  \LocPushpybrief{push-button-status.py}.}
\label{py:push-100}
\lstinputlisting{\LocPushpycode/push-button-status.py}
\end{pycode}

\begin{pycode}
\pcaption{Turning the LED on or off depending on the pushbutton}
  {Turning the LED on or off depending on the pushbutton.  Available at
  \LocPushpybrief{led-push-button.py}.}
\label{py:push-200}
\lstinputlisting{\LocPushpycode/led-push-button.py}
\end{pycode}