Python-3.4.3/C2/Getting-started-with-for/English

Python/C2/Getting-started-with-for/English

Title of script: Getting started with for loops

Author: Trupti, Thirumalesh H S

Keywords:Python, IPython, for loop, blocks, indent, iterate, loop

Visual Cue	Narration
Show Slide	Hello Friends. Welcome to the tutorial on "Getting started with for loops".
Show Slide Objectives	At the end of this tutorial, you will be able to, Use the for loop. Use range() function.
Show slide System Specifications	To record this tutorial, I am using Ubuntu Linux 14.04 operating system Python 3.4.3 IPython 5.1.0
Show Slide: Pre-requisite If not, see the relavant Python tutorials on http://spoken-tutorial.org	To practice this tutorial, you should know how to use lists. If not, see the relevant Python tutorials on this website.
	First let us see the syntax of for loop.
Show slide Syntax: For for <loop variable> in sequence:<statement 1> <statement 2> Body of for … <statement n> Highlight according to narration	for statement iterates over the members of a sequence in order, executing the block each time. Here the loop variable takes the value of the item inside the sequence on each iteration. For each item, the loop body is executed.
	We will see an example of ‘For’ loop and how to execute it.
[Terminal] ipython3	Let us first open the Terminal by pressing Ctrl+Alt+T keys simultaneously. Now, type ipython3 and press Enter.
[IPython console] %pylab and press Enter.	Let us initialise the pylab package. Type %pylab and press Enter.
	Open your text editor.
Highlight according to narration	Let us write a for loop. Type the code as shown here:
numbers = [4, 9, 16, 25, 36] for num in numbers: print(“sqrt of”, num, “is”, num**0.5) print("This is outside for-loop")	Here the for loop iterates over a list of numbers and finds the square root of each number. The numbers are: 4, 9, 16, 25, 36 Note that here we used two variables, numbers - which is a list of numbers num - which is the element of list under consideration in each cycle of the for loop. The variable names can be any of your choice.
Switch back to the editor.	Let us switch back to the text editor.
Highlight the line after for statement 2:22	Note that a colon after the for statement indicates the starting of loop body. Every statement in loop starts with 4 spaces
Highlight the line after for statement	It means that, the line is a block of code in for loop. In this example, it is only a single statement in the block.
Highlight the fifth line - print("This is outside for-loop")	Note that the line print("This is outside for-loop") is not indented. It means that it is not a part of the for loop. And the lines after that don't fall in the scope of the for loop.
Highlight indentation	Thus each block is separated by the indentation level. This marks the importance of white-spaces in Python.
	Save the file as sqrt_num_list.py in the home directory.
	Now switch back to your terminal.
[Ipython Terminal] Save & run script Highlight the output %run -i sqrt_num_list.py sqrt of 4 is 2.0 sqrt of 9 is 3.0 sqrt of 16 is 4.0 sqrt of 25 is 5.0 sqrt of 36 is 6.0 This is outside for-loop	Run the script using the run command as, percent run minus i filename and press Enter. We get the square root of the given numbers executed by the for loop. This is the print statement output executed after the for loop.
Show Slide Exercise 1	* Use the same example we used in sqrt_num_list.py Type each line of the code in the IPython interpreter prompt. Skip the line: print("This is outside for-loop")
[Ipython Terminal] numbers = [4, 9, 16, 25, 36] for num in numbers: Press Enter	Switch to the terminal. Type, numbers equal to inside square brackets 4, 9, 16, 25, 36 for num in numbers colon Press Enter
Highlight the dots	You will notice that, the prompt changes to three dots. And the cursor is not right after the three dots but, there are four spaces from the dots.
[Ipython Terminal] Highlight the three dots	Please note that IPython automatically indents the block. The three dots tell you that you are inside a block.
[Ipython Terminal] print(“sqrt of”, num, “is”, num**0.5)	Now type the rest of the for loop,print inside parentheses inside quotes sqrt of comma num comma inside quotes is comma num raised to power of 0.5
[Ipython Terminal]	Now we have finished the statements in the block. But still the interpreter is showing three dots, this means that you are still inside the block.
[Ipython Terminal] press Enter twice	To exit from the block press the Enter key twice without entering anything else.
[Ipython Terminal] Highlight output	It printed the square root of each number in the list, which was executed in the for loop.
	Next we will see about range built-in function in Python.
Show Slide range() function	Range() function generates a list of integers. The syntax is: range inside parentheses inside square brackets start comma close square brackets stop open square brackets comma step close square brackets For example: range inside parentheses one comma twenty comma two – generates integers from 1 to 19 with step of 2 range inside parentheses twenty – generates integers from 0 to 19
[Ipython Terminal] Highlight output	Note that the ending number that you specify will not be included in the list.
Show Slide Exercise 2	Find out the cube of all the numbers from one to ten Execute this in the Python interpreter.
[Terminal] python for i in range(1, 11): press Enter	Let us now try to run the for loop in a Python terminal window. Start the Python interpreter by issuing the command python in a new terminal. Type for i in range inside parentheses one comma eleven colon press Enter
[Python Terminal] Highlight the cursor	We will see that this time it shows three dots, but the cursor is close to the dots. So we have to indent the block.
[Python Terminal] print(i, "cube is", i**3)	The Python interpreter does not indent the code automatically. So enter four spaces there and then type the following print inside parentheses i comma inside quotes cube is comma i raised to power of three
[Python Terminal] press Enter	Now when we hit enter, we still see the three dots. To get out of the block, press Enter once again.
[Python Terminal]	Okay! so the main thing we learnt here is - how to use the Python interpreter and the IPython interpreter to specify blocks.
Show Slide Exercise 3	Print all the odd numbers from 1 to 50.
[IPython Terminal]	Let us do it in our IPython interpreter for ease of use. The problem can be solved by just using the range() function.
[IPython Terminal] for i in range(1, 51, 2): print(i) press Enter twice	for i in range inside parentheses one comma fifty one comma two colon print inside parentheses i and press Enter twice
[IPython Terminal] Highlight parameters in range function and highlight output	The first parameter is the starting number of the sequence. The second parameter is the end of the range.
Highlight third parameter	Note that the sequence does not include the ending number. The third parameter is for stepping through the sequence. Here we gave two which means we are skipping every alternate element.
Show Slide Summary	This brings us to the end of the tutorial. In this tutorial, we learnt to, Create blocks in python using for Indent the blocks of code Iterate over a list using for loop Use the range() function
Show Slide Assignment	Here are some self assessment questions for you to solve Indentation is not mandatory in Python True False 2. Write a for loop to print the product of all natural numbers from 1 to 20. 3. What will be the output of: range(1, 5)
Show Slide Solution of self assessment questions on slide	And the answers, False, Indentation is essential in python. 2. y equal to one for x in range inside parentheses one comma twenty one colon y into equal to x print inside parentheses y 3. range(1, 5) will produce a list of integers from 1 to 4 [1,2,3,4]
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.
Show Slide Textbook Companion	FOSSEE team coordinates the TBC project.
Show Slide Acknowledgment http://spoken-tutorial.org	Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India. For more details, visit this website.
Previous slide	This is _________ from IIT Bombay (or FOSSEE, if you wish) signing off. Thank you.

Contributors and Content Editors

Nancyvarkey, Nirmala Venkat, Trupti