Chandrika: Created page with '{| border=1 !Visual Cue !Narration |- | Show Slide 1 Containing title, name of the production team along with the logo of MHRD | Hello Friends and Welcome to the spoken tutori…'

2012-11-29T06:22:05Z

Created page with '{| border=1 !Visual Cue !Narration |- | Show Slide 1 Containing title, name of the production team along with the logo of MHRD | Hello Friends and Welcome to the spoken tutori…'

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!Visual Cue
!Narration
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Containing title, name of the production team along with the logo of MHRD
| Hello Friends and Welcome to the spoken tutorial on 'Using Python Modules'.

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| Show Slide 2

Learning objectives
| At the end of this tutorial, you will be able to ,

# Execute python scripts from command line.
# Use import in scripts.
# Import scipy and pylab modules.
# Use python standard modules and 3rd party modules.

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| Show Slide 3

Pre-requisite slide
| Before beginning this tutorial,we would suggest you to complete the tutorial on "Using plot interactively", "Embellishing a plot" and "Saving plots".

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| Show Slide 4

On running python scripts from command line
|

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| Let us create a simple python script to print hello world. Open your text editor and type the following,

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| Open the text editor and type the following

print "Hello world!"
print
|

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| Save the script as hello.py
| Now save this script as <tt>hello.py</tt>,

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| Open the terminal

ipython
| Start the ipython interpreter

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| %run -i hello.py
| In the previous tutorials,we have seen how to run a script using the IPython interpreter using <tt>%run</tt>

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| Close the terminal
| but this is not the correct way of running a python script.

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| Open terminal and navigate to directory where hello.py was saved
| The correct method is to run it using the Python interpreter. Open the terminal and navigate to the directory where hello.py is,

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| python hello.py
| now run the Python script as,

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| It executed the script and we got the output <tt>Hello World!</tt>.

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| Show Slide 5

Highlight <tt>python filename</tt> syntax on slide while narrating
| The syntax is <tt>python space filename</tt>.

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| Show Slide 6

Four plot problem
| Now, we have a four plot problem where we have plotted four plots in a single figure. Let us run that script from command line.

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| Open the four_plot.py file in text editor and show Pause for some time and then continue
| If you don't have the script, then make one with the following set of commands

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| python four_plot.py
| Now let us run four_plot.py as a python script.

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| Oops! even though it was supposed to work, it didn't. It gave an error <tt>linspace()</tt> is not defined, which means that the function <tt>linspace()</tt> is not available in the current name-space.

But if you try to run the same script using <tt>%run -i four_plot.py</tt> in your IPython interpreter started with the option <tt>-pylab</tt> it will work, because the <tt>-pylab</tt> option does some work for us by importing the required modules to our name-space when ipython interpreter starts. And thus we don't have to explicitly import modules.

So now let us try to fix the problem and run the script in command line,

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| Show Slide 7

fix <tt>linspace</tt> problem
| add this line as the first line in the script,

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| Add the line as first line in four_plot.py and save

from scipy import *
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| python four_plot.py
| Now let us run the script again,

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| Now it gave another error -- plot not defined,

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| Show Slide 8

| let us edit the file again and add this line as the second line in our script and save it,

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| add the line as second line in four_plot.py and save

from pylab import *
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| Switch to the terminal

python four_plot.py
| And now, run the script,

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| Yes! it worked. So what did we do?

We actually imported the required modules using the keyword <tt>import</tt>. It could also be done as by using,

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| Show Slide 9

Better way of fixing highlight the required line while narrating
| from scipy import linspace

instead of,

from scipy import *

So in practice it is always good to use function names instead of asterisk or star. If we use asterisk to import from a particular module then it will replace any existing functions with the same name in our name-space.

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| Show Slide 10

Instead of <tt><nowiki>*</nowiki></tt>
| So let us modify four_plot.py as, Hence we delete the first two lines of our code which we had added and add these lines

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| Switch to script 'four_plot.py' delete the first two lines and add the following

from scipy import linspace, pi, sin
from pylab import plot, legend, annotate
from pylab import xlim, ylim, title, show
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| python four_plot.py
| Now let us try running the code again as,

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| It works! In this method we actually imported the functions to the current name-space. There is one more way of doing it. And that is,

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| Show Slide 11

'another fix' highlight the required line while narrating
| Notice that we use <tt>scipy.pi</tt> instead of just <tt>pi</tt> as in the previous method, and the functions are called as <tt>pylab.plot()</tt> and <tt>pylab.annotate()</tt> and not as <tt>plot()</tt> and <tt>annotate()</tt>.

Pause the video here, try out the following exercise and resume the video.

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| Show Slide 12

Assignment 1
| Write a script to plot a sine wave from minus two pi to two pi. <nowiki><Pause> It can solved as,</nowiki>

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| Open sine.py and show it
| The first line we import the required functions <tt>linspace()</tt> , <tt>sin()</tt> and constant <tt>pi</tt> from the module scipy. The second and third line we import the functions <tt>plot()</tt>, <tt>legend()</tt>, <tt>show()</tt>, <tt>title()</tt>, <tt>xlabel()</tt> and <tt>ylabel()</tt>. And the rest the code to generate the plot.

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| Pause for sometime and then continue
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| Switch to the terminal

python sine.py
| We can run it as,

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| As we can see, we our sine plot. Let us move further in our topic.

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| Show Slide 13

What is a module?
| Until now we have been learning about importing modules, now what is a module?

A module is simply a file containing Python definitions and statements. Definitions from a module can be imported into other modules or into the main module.

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| Show Slide 14

Python standard library
| Python has a very rich standard library of modules. It is very extensive, offering a wide range of facilities. Some of the standard modules are,

for Math: math, random for Internet access: urllib2, smtplib for System, Command line arguments: sys for Operating system interface: os for regular expressions: re for compression: gzip, zipfile, tarfile And there are lot more.

Find more information at Python Library reference, <tt>http://docs.python.org/library/</tt>

There are a lot of other modules like pylab, scipy, Mayavi, etc which are not part of the standard python library.

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| Show Slide 15

Summary
| This brings us to the end of this tutorial. In this tutorial, we have learnt to,

# Run scripts from command line,
# Import modules by specifying the module name followed by an asterisk.
# Import only the required functions from modules by specifying the function name.
# Use python standard library.

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| Show Slide 16

Self assessment questions slide
| Here are some self assessment questions for you to solve

# Which among this is correct ?
** from scipy import plot
** from numpy import plot
** from matplotlib import plot
** from pylab import plot
# Which among these libraries is part of python standard library ?
** Mayavi
** scipy
** matplotlib
** urllib2
# Functions <tt>xlim()</tt> and <tt>ylim()</tt> can be imported to the current name-space as,
** from pylab import xlim, ylim
** import pylab
** from scipy import xlim, ylim
** import scipy

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| Show Slide 17

Solution of self assessment questions on slide
| And the answers,

# The option <tt>from pylab import plot</tt> is the correct one, since plot is a function of module module.
# <tt>urllib2</tt> is a part of the python standard library.
# Functions <tt>xlim()</tt> and <tt>ylim()</tt> can be imported to the current name-space as, <tt>from pylab import xlim, ylim</tt>.

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| Show Slide 18

Acknowledgment slide
| Hope you have enjoyed this tutorial and found it useful. Thank you!

|}

Python/C4/Using-python-modules/English - Revision history

Chandrika: Created page with '{| border=1 !Visual Cue !Narration |- | Show Slide 1 Containing title, name of the production team along with the logo of MHRD | Hello Friends and Welcome to the spoken tutori…'