.. Objectives

.. ----------

.. By the end of this tutorial you will be able to

.. #. Retrieve your ipython history 

.. #. View a part of the history 

.. #. Save a part of your history to a file. 

.. #. Run a script from within ipython 

.. Prerequisites

.. -------------

..   1. Embellishing Plots

.. Author              : Nishanth Amuluru

   Internal Reviewer   : 

   External Reviewer   :

   Checklist OK?       : <put date stamp here, if OK> [2010-10-05]

Script

------

Hello friends and welcome to the tutorial on Additional Features of IPython

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In this tutorial, we shall look at additional features of IPython that help us

to retreive the commands that we type on the interpreter and then save them

into a file and run it.

Let us start ipython with pylab loaded, by typing

::

    $ ipython -pylab

on the terminal

{{{ shift to terminal and type ipython -pylab }}}

We shall first make a plot and then view the history and save it.

::

    x = linspace(-2*pi, 2*pi, 100)

    plot(x, xsinx(x))

xsin(x) is actually x * sin(x)

::

    plot(x, x*sin(x))

    plot(x, sin(x))

    xlabel("x")

    ylabel("$f(x)$")   

    title("x and xsin")

We now have the plot. Let us look at the commands that we have typed in. The

history can be retreived by using =%hist= command. Type

::

    %hist

As you can see, it displays a list of recent commands that we typed. Every

command has a number in front, to specify in which order and when it was typed.

Please note that there is a % sign before the hist command. This implies that 

%hist is a command that is specific to IPython and not available in the vannila 

Python interpreter. These type of commands are called as magic commands.

Also note that, the =%hist= itself is a command and is displayed as the most

recent command. We should not that anything we type in is stored as history, 

irrespective of whether it is command or an error or IPython magic command.

If we want only the recent 5 commands to be displayed, we pass the number as an argument

to =%hist= command. Hence

::

    %hist 5 

displays the recent 5 commands, inclusive of the =%hist= command.

The default number is 40.

{{{ Pause here and try out the following exercises }}}

%% 1 %% Read through the documentation of %hist and find out how to

        list all the commands between 5 and 10

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As we can see from =%hist= documentation,

::

    %hist 5 10

displays the commands from 5 to 10

Now that we have the history, we would like to save the required line of code

from history. This is possible by using the =%save= command.

Before we do that, let us first look at history and identify what lines of code we require.Type

::

    %hist

{{{ point to the lines }}}

The first command is linspace. But second command is a command that gave us an

error. Hence we do not need second command. The commands from third to sixth are 

required. The seventh command although is correct, we do not need it since we

are setting the title correctly in the eigthth command.

So we need first third to sixth and the eigthth command for our program.

Hence the syntax of =%save= is

::

    %save /home/fossee/plot_script.py 1 3-6 8

{{{ point to the output of the command }}}

The command saves first and then third to sixth and eighth lines of code into

the specified file.

The first argument to %save is the path of file to save the commands and the

arguments there after are the commands to be saved in the given order.

{{{ goto the file and open it and show it }}}

{{{ Pause here and try out the following exercises }}}

%% 2 %% Change the label on y-axis to "y" and save the lines of code

        accordingly

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we use the command =ylabel= on interpreter as

::

    ylabel("y")

and then do

::

    %save /home/fossee/example_plot.py 1 3-6 10

Now that we have the required lines of code in a file, let us learn how to run

the file as a python script.

We use the IPython magic command =%run= to do this. Type

::

   %run -i /home/fossee/plot_script.py

The script runs but we do not see the plot. This happens because when we are running

a script and we are not in interactive mode anymore.

Hence on your terminal type

::

    show()

to show the plot.

{{{ Pause here and try out the following exercises }}}

%% 3 %% Use %hist and %save and create a script that has show in it and run it

        to produce and show the plot.

{{{ continue from paused state }}}

We first look at the history using

::

    %hist 20

Then save the script using

::

    %save /home/fossee/show_included.py 1 3-6 8 10 13

    %run -i /home/fossee/show_included.py

    show()    

We get the desired plot.

The reason for including a -i after run is to tell the interpreter that if any

name is not found in script, search for it in the interpreter. Hence all these

sin, plot, pi and show which are not available in script, are taken from the

interpreter and used to run the script.

{{{ Pause here and try out the following exercises }}}

%% 4 %% Run the script without using the -i option. Do you find any difference?

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We see that it raises NameError saying that the name linspace is not found.

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This brings us to the end of the tutorial.

we have looked at 

 * Retreiving history using =%hist= command

 * Vieweing only a part of history by passing an argument to %hist

 * saving the required lines of code in required order using %save

 * using %run -i command to run the saved script

{{{ Show the "sponsored by FOSSEE" slide }}}

This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India

Hope you have enjoyed and found it useful.