Python-3.4.3/C3/Conditional-Statements/English

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Visual Cue
Narration
Show Slide title Welcome to the spoken tutorial on Conditional statements.
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Objectives


In this tutorial, we will learn to use
  • if/else blocks
  • if/elif/else blocks
  • Ternary conditional statement and
  • Pass statement


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System Specifications

To record this tutorial, I am using


  • Ubuntu Linux 16.04 operating system
  • Python 3.4.3
  • IPython 5.1.0


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Pre-requisite


To practice this tutorial, you should know how to use


  • basic data types and operators
  • strings and Input/Output statements

If not, see the relevant Python tutorials on this website.

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if condition


First let us learn about if condition.


if condition is used to decide whether to execute the statements in the if block or not.


Here is the syntax.

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if else condition

Box line by line


Highlight :


Highlight 4 spaces

Next we will see about if else condition.


When the test condition is true, it will execute the body of if.


If the condition is False, body of the else is executed.


Note that, if and else statements end with a colon.


This denotes the beginning of the code block of True or False condition.


All the statements inside a code block are indented by 4 spaces.

Open the terminal Let us start ipython.


Open the terminal.

Type ipython3

press Enter

Type ipython3 and press Enter.


From here onwards, remember to press the Enter key after typing every command on the terminal.

Type: num = int(input())


Enter number 4 and press Enter

Now let us check if an entered number is even or not.


Type, num is equal to int inside brackets input open and close brackets


Enter 4 and press Enter

Type

if num % 2 == 0: print ('Even')else: print ('Odd')


Highlight the output


HIghlight the spaces

Type, if num percentage 2 equal to equal to 0 colon

print inside brackets inside single quotes Even


Press backspace four times and type, else colon

print inside brackets inside single quotes Odd


Press Enter twice to get the output.


As expected, it displays Even as output.


Note that, the statements inside a code block are indented by 4 spaces automatically.


<<PAUSE>>

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elif statement


Next we will see another conditional statement called elif.


All the syntax and rules for elif are same as if/else statements.


In if/else, only one condition is checked.


But in elif statement multiple conditions can be checked.

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if/elif Example


Box line by line

For example,


The first block of code is executed as soon as condition one evaluates to True.


All the subsequent conditions in elif ladder are not checked.


The else block gets executed if all the conditions in if and elif ladder are evaluated to False.

Type a = -3

if a > 0:

print ("positive")

elif a < 0:

print ("negative")

else:

print ("zero")


Highlight positive

Highlight negative

Highlight zero

Let us understand if/elif/else ladder with an example.


Type, a is equal to minus 3


We have a variable a which holds integer value as -3.


Type as shown.


This program will print

  • "positive" if a is positive,
  • "negative" if it is negative or
  • "zero" the above conditions are evaluated to False

Press Enter twice to see the output.

Show Slide if/elif example

Highlight elif

We can also have any number of elif conditions within an if/elif/else statements.


For example, based on the type of user the corresponding operations are performed using elif.

Pause the video.


Try this exercise and then resume the video.

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Assignment 1

Given a number, num as input.


Write an if else block to print num, if it is divisible by 10, else print 10 asterisk num.

Show Slide Solution 1 The solution is on your screen.


<<PAUSE>>

Slide:

Ternary operator

syntax:

[A] if <condition> else [B]


Next let us learn about ternary operator.


Ternary operator allows to test a condition in a single line replacing the multiline if-else.


It can reduce the code size and increase the readability of the code.


Here is the syntax.

Type, a = 4 Let us write a ternary conditional statement to find the largest of two numbers.


Type, a is equal to 4

Type, b = 2 b is equal to 2
Type, large_num = a if a > b else b large underscore num is equal to a if a greater than b else b
Type, print(large_num) print inside brackets large underscore num


We got the required output.

Pause the video.


Try this exercise and then resume the video.

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Assignment 2

Given a number, n as input.


Write a ternary operator to print n, if it is divisible by 10, else print 10 asterisk n.

Show Slide Solution 2 The solution is on your screen.


<<PAUSE>>

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Pass statement


Next we will learn about pass statement.

The pass statement acts as a null operation (i.e) nothing happens when it executes.


It works as a placeholder for a block of code.


It is used in a code block where actual code implementation is not known yet.

Type a = 11 Let us understand the pass statement with an example.


Type a is equal to 11

Type,

if a%2 == 0: print(‘even’)else: pass

Then type as shown.


If a divided by 2 equals to zero, if block is executed.

Else no operation is performed.


Press Enter key twice to get the output.


Here a divided by 2 is not 0.


So no operation is performed and nothing is displayed as output.

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Summary


This brings us to the end of the tutorial.


Let us summarize.


In this tutorial, we have learnt the conditional statements such as,

  • if/else statement
  • if/elif/else statement
  • Ternary conditional statement and
  • Pass statement

<<PAUSE>>

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Evaluation


Here are some self assessment questions for you to solve.


1. Given a variable t.

Print Good Morning if it is less than 12, otherwise print Hello. Use if else statement.


2.Convert the below if else code into ternary conditional statement.

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Solutions

And the answers,
  1. The following code gives the required output.
  2. Use the following statement to convert the if else code into a ternary statement


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.
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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 Priya from IIT Bombay signing off. Thanks for watching.

Contributors and Content Editors

Nancyvarkey, Priyacst