Conditional Operators:
The Python ternary operator (or conditional operator), tests if a condition is true or false and, depending on the outcome, returns the corresponding value — all in just one line of code. Below are some of the conditional operators:
| Conditional Operators | Conditional Operators | Conditional Operators |
| Greater than > | Greater than equal to >= | Equal to == |
| Less than < | Less than equal to <= | Not equal to != |
Example:
a = int(input("Enter your age: ")) #output: Enter your age: 18
print("Your age is: ", a) #output: Your age is: 18
print(a>18) #output: False
print(a<=18) #output: True
print(a==18) #output: True
print(a!=18) #output: False
Based on this, the conditional statements are further classified into following types:
if
if-else
if-else-elif
nested if-else-elif.
if-else statement:
Sometimes the programmer needs to check the evaluation of certain expression(s), whether the expression(s) evaluate to True or False.
If the expression evaluates to False, then the program execution follows a different path than it would have if the expression had evaluated to True.
Syntax:
if LOGIC:
TRUE_body
else:
FALSE_Body
# Note: LOGIC = TRUE | False
Example 01:
a = int(input("Enter your age: "))
print("Your age is: ", a)
if(a>18):
print("You can drive")
print("Yes")
else:
print("You cannot drive")
print("No")
print("Yay!") #no indentation here - means it prints every time
Output :
#if input = 9
Enter your age: 9
Your age is: 9
You cannot drive
No
Yay!
#if input = 76
Enter your age: 76
Your age is: 76
You can drive
Yes
Yay!
Example 02:
applePrice = 210
budget = 200
if (applePrice <= budget):
print("Alexa, add 1 kg Apples to the cart.")
else:
print("Alexa, do not add Apples to the cart.")
Output:
Alexa, do not add Apples to the cart.
elif Statements:
Sometimes, the programmer may want to evaluate more than one condition, this can be done using an elif statement.
Example 01:
applePrice = 10
budget = 200
if (budget - applePrice):
print("Alexa, add 1 kg Apples to the cart.")
elif(budget - applePrice > 70):
print("Its okay you can buy")
else:
print("Alexa, do not add Apples to the cart.")
Output:
Alexa, add 1 kg Apples to the cart.
Example 02:
num = int(input("Enter the value of num: "))
if (num < 0):
print("Number is negative.")
elif (num == 0):
print("Number is Zero.")
elif (num == 999):
print("Number is Special.")
else:
print("Number is positive.")
print("I am happy now")
Output:
If input = 7
Enter the value of num: 7
Number is positive.
I am happy now
if input = -8
Enter the value of num: -8
Number is negative.
I am happy now
if input = 0
Enter the value of num: 0
Number is Zero.
I am happy now
if input = 999
Enter the value of num: 999
Number is Special.
I am happy now
Nested if Statements:
We can use if, if-else, elif statements inside other if statements as well.
Example:
num = 18
if (num < 0):
print("Number is negative.")
elif (num > 0):
if (num <= 10):
print("Number is between 1-10")
elif (num > 10 and num <= 20):
print("Number is between 11-20")
else:
print("Number is greater than 20")
else:
print("Number is zero")
Output:
Number is between 11-20
Quiz Questions:
Create odd and even number program using if else statements.
Create a program of Grading System using elif statements.
Create username and password system using if else statements.
Answer: Will provided in next lecture...
Key Points:
Indentation in python - means we enter in a 'block' line.
Level of indentation - means under indentation there is another indentation.