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if...else

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Python If ... Else

Python supports the usual logical conditions from mathematics:

  • Equals: a == b

  • Not Equals: a != b

  • Less than: a < b

  • Less than or equal to: a <= b

  • Greater than: a > b

  • Greater than or equal to: a >= b

These conditions can be used in several ways, most commonly in "if statements" and loops.

An "if statement" is written by using the if keyword.

Example

If statement:

a = 10
b = 20
if b > a:
    print("b is greater than a")

Output:    
    b is greater than a

In this example we use two variables, a and b, which are used as part of the if statement to test whether b is greater than a. As a is 10, and b is 20, we know that 20 is greater than 10, and so we print to screen that "b is greater than a".

 

Note: Note that in if block indentation is most important, if you do not keep indentation, then above program will not execute, it will give an error

a = 10
b = 20
if b > a: 
print("b is greater than a")

Above program will give an error like

IndentationError: expected an indented block

elif

The elif keyword is pythons way of saying "if condition is not correct then it will execute else part.

a = 10
b = 10
if b > a:          
    print("b is greater than a")
elif a == b:          
    print("a and b are equal")

#Output:    
a and b are equal

In the above case, if first b>a condition is not true then else condition a==b will execute.

Else:

The else case will execute if all above conditions are not true.

a = 10
b = 20
if a > b:          
    print("b is greater than a")
elif a == b:          
    print("a and b are equal")
else:          
    print("a is greater than b")

Output:        
    a is greater than b

If-else:

    You can also have an else without the elif:

a = 10
b = 20
if a > b:          
    print("b is greater than a")
else:          
    print("b is not greater than a")

Output:    
    b is not greater than a

Lab Assignment:

Write a python program to check given year is a leap year or not.

year=int(input("Enter  Year : "))

if(year%4==0):
        if(year%100==0):
            if(year%400==0):
                print(year," is a Leap Year")
            else:
                print(year, "is not a Leap Year")
        else:
            print(year," is not a Leap Year")
    else:
        print(year," is not a Leap Year")

#Output
Enter  Year : 2000
2000 is a Leap year