Python if else elif Statement

• Python if-elif-else statement is used to write a conditional flow code.
• The statements are in the order of if…elif…else.
• The ‘elif’ is short for ‘else if’ statement. It’s shortened to reduce excessive indentation.
• The else and elif statements are optional.
• There can be multiple elif statements.
• We can have only one else block for an if statement.
• The if, else, and elif are reserved keywords in Python.
• Python doesn’t have switch-case statements like other languages. The if-else conditions are sufficient to implement the control flow in the Python scripts.
• We can have nested if-else blocks in Python.
• Python ternary operation allows us to write an if-else statement in a single line. It’s useful when the if-else condition is simple and we want to reduce the code length.

Python if else Syntax

The general syntax if if-else statement in Python is:

if condition:
    # code
elif condition:
    # code
... # multiple elif statements
else:
    # default code

1. Every if-elif statement is followed by a condition.
2. If the condition evaluates as True, then the code in that block gets executed.
3. Once the code in any of the block is executed, the control flow moves out of the if-elif-else block.
4. If none of the conditions are True, then the else block code is executed.

Python if-elif-else Example

Let’s say we have a function that accepts a country name and return its capital. We can implement this logic using if-else conditions.

def get_capital(country):
    if country == 'India':
        return 'New Delhi'
    elif country == 'France':
        return 'Paris'
    elif country == 'UK':
        return 'London'
    else:
        return None

Earlier, we mentioned that elif statement is optional. Let’s look at another simple example where we don’t have elif statement.

def is_positive(num):
    if num >= 0:
        return 'Positive'
    else:
        return 'Negative'

Even the else block is optional. Let’s look at another example where we have only if condition.

def process_string(s):
    if type(s) is not str:
        print('not string')
        return
    # code to process the input string

In case you are wondering what is with empty return statement, it will return None to the caller.

Python if-else in One Line

Let’s say we have a simple if-else condition like this:

x = 10

if x > 0:
    is_positive = True
else:
    is_positive = False

We can use Python ternary operation to move the complete if-else block in a single line.

The syntax of ternary operation is:

value_true if condition else value_false

Let’s rewrite the above if-else block in one line.

is_positive = True if x > 0 else False

Nested if-else Conditions

We can have multiple nested if-else conditions. Please be careful with the indentation, otherwise the result might be unexpected.

Let’s look at a long example with multiple if-else-elif conditions and nested to create an intelligent number processing script.

# accepting user input
x = input('Please enter an integer:\n')

# convert str to int
x = int(x)

print(f'You entered {x}')

if x > 0:
    print("It's a positive number")
    if x % 2 == 0:
        print("It's also an even number")
        if x >= 10:
            print("The number has multiple digits")
    else:
        print("It's an odd number")
elif x == 0:
    print("Lovely choice, 0 is the master of all digits.")
else:
    print("It's a negative number")
    if x % 3 == 0:
        print("This number is divided by 3")
    if x % 2 == 0:
        print("And it's an even number")
    else:
        print("And it's an odd number")

Here are the sample output from multiple iterations of this code.

Please enter an integer:
10
You entered 10
It's a positive number
It's also an even number
The number has multiple digits

Please enter an integer:
0
You entered 0
Lovely choice, 0 is the master of all digits.

Please enter an integer:
-10
You entered -10
It's a negative number
And it's an even number

Conclusion

Python if-else condition allows us to write conditional logic in our program. The syntax is simple and easy to use. We can use ternary operation to convert simple if-else condition into a single line. Please be careful with the indentation when you have multiple nested if-else conditions.