Python-3.4.3/C4/Writing-Python-Scripts/English

Title of script: Writing Python scripts

Author: Aditya Palaparthy, Arun KP

Keywords: Python, Ipython, python script, import module, name variable, video tutorial

Visual Cue	Narration
Show Slide title	Welcome to the spoken tutorial on Writing Python scripts.
Show Slide Objectives	In this tutorial we will learn, What is importing Write your own Python modules and Understand the double underscore name double underscore double equal to within double quotes double underscore main double underscore idiom
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 Run basic Python commands on the IPython console and Use Python modules. If not, see the relevant Python tutorials on this website.
Show Slide Python Modules	We can write Python modules to bundle functions. We can then make use of these functions by importing modules to other scripts.
	Let us first write a function and save it in a script.
Open an editor and type the following code def gcd(a, b): while b: a, b = b, a%b return a if gcd(40, 12) == 4: print ("Everything is OK") else: print ("The GCD function is wrong")	Open any text editor and type the below code.
Highlight def gcd(a, b): while b: a, b = b, a%b return a Highlight if gcd(40, 12) == 4: print ("Everything is OK") else: print ("The GCD function is wrong")	This Python module has a function to compute gcd of two numbers. Please take care of the indentation. We have included a test case in the script. This test case will check the gcd function every time the script is run.
Save the script as gcd_script.py	Let us save the file as gcd underscore script.py in the current working directory.
Type ipython3	Open a new terminal. Type, ipython3 and press Enter.
	From here onwards remember to press the Enter key after typing every command on the terminal.
Type, %run gcd_script.py Highlight the output “Everything is OK”	Now we will run the script. Type, percentage run gcd underscore script.py We get an output which says “Everything is OK”.
Switch to the gcd_script.py	It means that the test case checking gcd inside brackets 40 comma 12 equals to 4 is passed. What if we want to use the gcd function in some other scripts? This is possible since every Python file can be used as a module.
Type, import sys	But first, we will understand what happens when we import a module. Type, import sys
Type, sys.path	Now type sys.path
Highlight the output Highlight the empty string	We can see a list of locations. This indicates that Python searches for a module when it encounters an import statement. The standard modules are built into Python itself. Otherwise it is found in system locations like slash usr slash lib slash python3.4 slash The first item in the list is an empty string. It means the current working directory is also searched.
Type, import gcd_script Highlight Everything is OK Type, print("gcd of 187 and 391 is", gcd_script.gcd(187, 391)) Highlight gcd of 187 and 391 is 17	We can import a module present in the current working directory. Type, import gcd underscore script Since gcd underscore script.py is in the current working directory, import will work directly. Type the print statement as shown here. We get the gcd of 187 and 391 as output, which is 17.
Highlight Everything is OK	We can also see the output “Everything is OK” that we added as test code. This is also executed when we imported gcd underscore script. The test code is added to check the gcd function.
Slide: __name__ variable. Highlight __name__	Test code should only be executed when we run the Python script independently. To execute the test code when the module is imported to other scripts, we can use double underscore name double underscore variable. Hereafter I will call this as name variable.
Switch to gcd_script.py Add if __name__ == "__main__": after the line return a	First, we shall look at how to use the variable and then understand how it works. Now we will add this variable in the script gcd underscore script.py Type the following after return a statement if double underscore name double underscore double equal to inside double quotes double underscore main double underscore colon Indent the code properly.
Save the file	Save the file.
Type %run gcd_script.py Highlight Everything is OK	Let us run the code. Type, percentage run gcd underscore script.py We can see that the test is executed successfully and we get output as Everything is OK
Type, import gcd_script Type, exit	Now we will check the changes by importing the module. Type,import gcd_script We didn’t see any changes. Note that, once a module is imported, it cannot be imported again in an existing IPython console. So we will exit the existing IPython console by typing exit.
Open terminal and type ipython3	Open another terminal. Type ipython3.
Type import gcd_script	Now we will import gcd underscore script.py. Type, import gcd underscore script We can see that now the test code is not executed. Everything is OK is not displayed as output.
Open gcd_script.py and highlight the if __name__ == "__main__": block in the file gcd_script.py	The name variable is local to every module. It is equal to main only when the file is run as a script. Hence, all the code under the block, if name double equal to within double quotes main is executed only when the file is run as a Python script.
Switch terminal	Switch back to the terminal.
Type, from gcd_script import gcd def check_relative_prime(a,b): if gcd(a,b)==1: print("Yes, %d and %d are relatively prime" %(a,b)) else: print("No, %d and %d are not relatively prime" %(a,b)) check_relative_prime(11,3) Highlight Yes, 11 and 3 are relatively prime	Type the following code which checks whether two numbers are relatively prime. We have imported gcd function from gcd underscore script. And use it in our calculations without the test code being executed. Two numbers are relatively prime when their gcd is equal to one. So we get output as Yes, 11 and 3 are relatively prime.
Slide	Every Python file can be run in two ways: As an independent stand-alone script or As a Python module which can be imported by other Python scripts or modules.
Show Slide Summary slide	This brings us to the end of this tutorial. Let us summarize. In this tutorial, we have learnt to, Import a module Use a script as a module Write test condition using the name variable Restart IPython3 if a changed module is to be imported again.
Show Slide Evaluation	Here are some self assessment questions for you to solve Which of the following variables contains the locations to search for Python modules A module should contain only one function. True or False
Show Slide Solutions	And the answers. sys.path contains the locations to search for Python modules. False. A module can contain a wide range of functions.
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 Acknowledgement	Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India. For more details, visit this website.
Show Slide Thank You	This is Priya from IIT Bombay signing off. Thanks for watching.

Contributors and Content Editors

Nancyvarkey, Nirmala Venkat, Priyacst