Python/C3/Conditionals/English
| 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 tutorial on 'Conditionals'. |
| Show Slide 2
Learning objectives |
At the end of this tutorial, you will be able to,
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Shift to terminal and start ipython
ipython |
To begin with let us start ipython, |
| a = 5 | Whenever we have two possible states that can occur depending on a a certain condition, we can use if/else construct in Python.
For example, say, we have a variable a which stores integers and we are required to find out whether a is even or odd. Let's say the value of a is 5. |
if a % 2 == 0:
print "Even"
else:
print "Odd"
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In such a case we can write the if/else block as |
| If a is divisible by 2, i.e., the result of "a modulo 2" is 0, it prints "Even", otherwise it prints "Odd".
Note that in such a case, only one of the two blocks gets executed depending on whether the condition is True or False. There is a very important syntactic element to understand here. Every code block begins with a line that ends with a :, in this example the if and the else lines. Also, all the statements inside a code block are intended by 4 spaces. Hitting enter twice, ends the code block. The if/else blocks work for a condition, which can take one of two states. But what do we do for conditions, which can take more than two states? | |
a = -3
if a > 0:
print "positive"
elif a < 0:
print "negative"
else:
print "zero"
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Python provides if/elif/else blocks, for such conditions. For example. We have a variable a which holds integer values. We need to print "positive" if a is positive, "negative" if it is negative or "zero" if it is 0.
Let us use if/elif/else ladder for it. For the purposes of testing our code let us assume that the value of a is -3 |
| All the syntax and rules as said for if/else statements hold the same. The only addition here is the elif statement which can have another condition of its own.
Here too, exactly one block of code is executed -- the block of code which first evaluates to True. Even if there is a situation where multiple conditions evaluate to True, all the subsequent conditions other than the first one, which evaluates to True, are neglected. Consequently, the else block gets executed if and only if all the conditions evaluate to False. | |
| Show Slide 3
~if/elif~ ladder if user == 'admin': # Do admin operations elif user == 'moderator': # Do moderator operations elif user == 'client': # Do customer operations |
Also, the else block in both if/else statement and if/elif/else is optional. We can have a single if statement or just if/elif statements without having else block at all. Also, there can be any number of elif's within an if/elif/else ladder. For example |
| Note that there are multiple elif blocks and there is no else block.
Pause the video here, try out the following exercise and resume the video. | |
| Show Slide 4
Assignment 1 |
Given a number, num. Write an if else block to print num, as is,
if it is divisible by 10, else print 10 * num. |
| Show Slide 5
Solution 1 if num%10 == 0: print num else: print 10*num |
The solution is on your screen. |
| score_str = 'AA' | In addition to these conditional statements, Python provides a very convenient ternary conditional operator. Let us take the following example where we read the marks from a data file which is obtained as a string as we read a file. The marks can be in the range of 0 to 100 or 'AA' if the student is absent. In such a case, to obtain the marks as an integer, we can use the ternary conditional operator. Let us say the string score is stored in score_str variable |
| score = int(score_str) if score_str != 'AA' else 0 | Now let us use the ternary conditional operator |
| Show Slide 6
Assignment 2 |
Given a number, num. Write a ternary operator to print num, as is,
if it is divisible by 10, else print 10 * num. |
| Show Slide 7
Solution 2 |
The solution is on your screen.
print num if num%10 == 0 else 10*num |
| Moving on, there are certain situations where we will have no operations or statements within a block of code. For example, we have a code where we are waiting for the keyboard input. If the user enters "c", "d" or "x" as the input, we would perform some operation; nothing otherwise. In such cases "pass" statement comes very handy | |
| Show Slide 8
Pass statement |
a = raw_input("Enter 'c' to calculate and exit, 'd' to display the existing
results exit and 'x' to exit and any other key to continue: ") if a == 'c': # Calculate the marks and exit elif a == 'd': # Display the results and exit elif a == 'x': # Exit the program else: pass |
| In this case "pass" statement acts as a place holder for the block of code. It is equivalent to a null operation. It literally does nothing. It can used as a place holder when the actual code implementation for a particular block of code is not known yet but has to be filled up later. | |
| Show Slide 9
Summary slide |
This brings us to the end of the tutorial. In this tutorial, we have learnt to,
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| Show Slide 10
Self assessment questions slide |
Here are some self assessment questions for you to solve
Enumerated list ends without a blank line; unexpected unindent. x = 20
if x > 10:
print x * 100
else:
print x
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| Show Slide 11
Solution of self assessment questions on slide |
And the answers,
1. We can use the if/else statements as if time < 12:
print "Good Morning"
else:
print "Hello"
Enumerated list ends without a blank line; unexpected unindent. print x * 100 if x > 10 else x |
| Show Slide 12
Acknowledgment slide |
Hope you have enjoyed this tutorial and found it useful. Thank you! |
