Python-3.4.3/C4/Using-Python-Modules/English

Title of script: Using Python Modules

Author: Puneeth, Aditya Palaparthy, Thirumalesh H S,Arun KP

Keywords: Python, Ipython, scripts, import, plot, modules, video tutorial

Visual Cue	Narration
Show Slide containing title	Welcome to the spoken tutorial on Using Python Modules.
Show Slide Learning Objectives	In this tutorial, you will learn to- Execute Python scripts from command line Use import in scripts and Import numpy and matplotlib.pyplot modules
Show Slide System Specifications	To record this tutorial, I am using Ubuntu Linux 16.04 operating system Python 3.4.3 IPython 5.1.0 and Gedit text editor
Show Slide Prerequisite slide	To practise this tutorial, you should know how to Use plot interactively Embellish and save a plot If not, see the relevant Python tutorials on this website.
Show Slide What is a module?	First we will learn what is a module. A module is a file containing Python definitions and statements. Modules are used to break down large programs into small manageable and organized files. Definitions from a module can be imported into other modules or to the main module.
Open text editor Type, print ("Hello World")	Now let us see how to run a Python script from command line. Open any text editor and type, print inside brackets inside double quotes Hello World We have created a simple Python script to print Hello World.
Save the script as hello.py	Save this script as hello.py in the current working directory.
Open terminal and navigate to directory where hello.py was saved	Now let us open the terminal. Then navigate to the directory where hello.py is saved.
Type, python3 hello.py	Now type, python3 hello.py and press Enter. It executes the script and gives the output as Hello World.
	From here onwards, remember to press the Enter key after typing every command on the terminal.
Open the four_plot.py file in text editor and show	Next we will see how to import modules and use them in Python scripts. Let me open the file four underscore plot.py in the text editor. This file is available in the Code files link of this tutorial. You can download and use it.
Highlight the 4 plot command	This code will plot for x, -x, sin of x and xsin of x
Show slide Four plot Problem	When we run this code, we will see the final plot as shown here.
Type, python3 four_plot.py	Now let us run the file four underscore plot.py as a Python script. Type, python3 four underscore plot.py It gives an error linspace() is not defined. It means that, function linspace() is not available in the current namespace. A namespace is a system for making all the names in a program to be unique.
Switch to four_plot.py	Let us go back to the file four underscore plot.py.
Add the line as first line in four_plot.py and save from numpy import * Highlight linspace	Add this line as the first line in the script, from numpy import asterisk When we use asterisk in imports, all the functions and constants are imported from numpy module. linspace is a function available in numpy.
Save the file	Press Ctrl + S to save the file.
Type, python3 four_plot.py	Now let us run the script again. Now it gave another NameError: name ‘plot’ is not defined.
Open four_plot.py in text editor	Let us edit the four underscore plot.py file again. Add the following as the second line in our script. from matplotlib.pyplot import *
	Now save the file.
Save the file	plot is a function which is available in the matplotlib.pyplot.
python3 four_plot.py	We will run the script again. We get the output now. We imported all the required modules using the keyword import.
Close the window	Let me close this window.
Show Slide Import functions	We can import only functions which are required from a module as, from numpy import linspace, pi, sin instead of, from numpy import *
Show Slide Import functions	In the same way we can import only required functions from matplotlib.pyplot instead of, from matplotlib.pyplot import *
slide : Import Functions	It is always good to use function names instead of asterisk. If we use asterisk to import from a particular module, all the functions will be imported. It replaces some existing functions with the same name in the namespace.
Switch to script 'four_plot.py' delete the first two lines and add the following from numpy import linspace, pi, sin from matplotlib.pyplot import plot, legend, annotate from matplotlib.pyplot import xlim, ylim, title, show	Now we will add only required functions from numpy and matplotlib.pyplot
Save the file	Let us save the file.
python3 four_plot.py	We will run the code again in the terminal. Here, we got the plots for x, -x, sin of x and xsin of x in a single figure. In this method we imported all the required functions to the current namespace.
	There is another way of fixing errors. Let us see that.
Highlight import matplotlib.pyplot as plt Highlight numpy.pi in line 3 and line 10, 11 plt.plot in line 4 plt.legend in line 8 plt.annotate in line 9 plt.xlim, plt.ylim in line 10 and 11 plt.show() in line 12	Open the file another underscore fix.py This file is also available in the Code files link of this tutorial. Notice that we are going to use the name plt instead of matplotlib.pyplot. plt is used as alias to the module matplotlib.pyplot Now, we use numpy.pi instead of just pi as we did in four underscore plot.py. Plot functions are called as plt.plot() plt.legend() plt.annotate() plt.xlim plt.ylim plt.show() The advantage is that function names in imported modules do not get added to the current namespace. In order to use a function in an imported module, we need to mention module-name.function-name
Show Slide Exercise 1	Pause the video here. Try this exercise and then resume the video. Write a python script to plot a sine wave from -2pi to 2pi.
show text for codefiles Open sine.py and show it	Open the file sine.py for the solution. This file is also available in the Code files link. In the first line we import the required functions. The functions linspace, sin and constant pi are imported from the module numpy. We import the functions plot, legend, show, title, xlabel and ylabel from matplotlib.pyplot. And the rest of the code is to generate the plot.
Type, python3 sine.py	Let us run the code and see the output. In the terminal, type python3 sine.py Now we can see our sine plot. Close the terminal. Let us move further in our topic.
Type, ipython3	We can run Python scripts in IPython interpreter also. Open another terminal and start the ipython interpreter by typing ipython3
Type, %run four_plot.py	Navigate to the directory where four underscore plot.py is saved and type percentage run four underscore plot.py As before we can see the output with 4 plots.
Show Slide Python standard library	Python has a very rich standard library of modules. Some of the standard modules are, for Math: math, random for Internet access: urllib2, smtplib for System and Command line arguments: sys
Show Slide Python standard library	Few more libraries for Operating system interface: os for regular expression: re for compression: gzip, zipfile, tarfile For more information refer to the below link.
Show Slide Summary	This brings us to the end of this tutorial. Let us summarize. 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.
Show Slide Evaluation	Here are some self assessment questions for you to solve Which among the below is the most correct? How the functions xlim() and ylim() can be imported to the current namespace?
Show Slide Solutions	And the answers, The option from matplotlib.pyplot import plot is the most correct one. Because plot is a function of matplotlib.pyplot module. Functions xlim() and ylim() can be imported to the current namespace as, from matplotlib.pyplot import xlim, ylim
Show Slide Forum	Please post your timed queries in this forum.
Show Slide Fossee Forum	Please post your general queries on Python in this forum.
Slide Textbook Companion	FOSSEE team coordinates the TBC project.
Show Slide Acknowledgment	Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India. For more details, visit this website.
Previous slide	This is Priya from IIT Bombay signing off. Thanks for watching.

Contributors and Content Editors

Nancyvarkey, Nirmala Venkat, Priyacst