CONDITIONAL STATEMENTS IN PYTHON

PYTHON CONDITIONAL STATEMENTS

There are situations in real life when we need to make some decisions and based on these decisions, we decide what we should do next. Similar situations arise in programming also where we need to make some decisions and based on these decisions we will execute the next block of code.

Conditional statements in Python languages decide the direction(Control Flow) of the flow of program execution.

Types of Statements in Python

There are 4 types of Statements in Python...

1. The if statement

2. The if-else statement

3. The nested-if statement

4. The if-elif-else ladder

if statement

The if statement is the most simple decision-making statement. It is used to decide whether a certain statement or block of statements will be executed or not.

Syntax:

if condition:

# Statements to execute if

# condition is true

Here, the condition after evaluation will be either true or false. if the statement accepts boolean values-if the value is true then it will execute the block of statements below it otherwise not.

As we know, python uses indentation to identify a block. So the block under an if statement will be identified as shown in the below example:

if condition:

statement1

statement2

# Here if the condition is true, if block

# will consider only statement1 to be inside

# its block.

Example:

As the condition present in the if statement is false. So, the block below the if statement is executed.

# python program to illustrate If else statement

#!/usr/bin/python

i = 20

if (i < 15):

print("i is smaller than 15")

print("i'm in if Block")

else:

print("i is greater than 15")

print("i'm in else Block")

print("i'm not in if and not in else Block")

Output:

i is greater than 15

i'm in else Block

i'm not in if and not in else Block

if-else Statement

The if statement alone tells us that if a condition is true it will execute a block of statements and if the condition is false it won’t. But if we want to do something else if the condition is false, we can use the else statement with the if statement to execute a block of code when the if condition is false.

Syntax:

if (condition):

# Executes this block if

# condition is true

else:

# Executes this block if

# condition is false

Example:

The block of code following the else statement is executed as the condition present in the if statement is false after calling the statement which is not in the block(without spaces).

# Explicit function

def digitSum(n):

dsum = 0

for ele in str(n):

dsum += int(ele)

return dsum

# Initializing list

List = [367, 111, 562, 945, 6726, 873]

# Using the function on odd elements of the list

newList = [digitSum(i) for i in List if i & 1]

# Displaying new list

print(newList)

Output :

[16, 3, 18, 18]

Nested-if Statement

A nested if is an if statement that is the target of another if statement. Nested if statements mean an if statement inside another if statement.

Yes, Python allows us to nest if statements within if statements. i.e., we can place an if statement inside another if statement.

Syntax:

if (condition1):

# Executes when condition1 is true

if (condition2):

# Executes when condition2 is true

# if Block is end here

Example:

In this example, we are showing nested if conditions in the code, All the If conditions will be executed one by one.

# python program to illustrate nested If statement

i = 10

if (i == 10):

# First if statement

if (i < 15):

print("i is smaller than 15")

# Nested - if statement

# Will only be executed if statement above

# it is true

if (i < 12):

print("i is smaller than 12 too")

else:

print("i is greater than 15")

Output:

i is smaller than 15

i is smaller than 12 too

if-elif-else Ladder

Here, a user can decide among multiple options. The if statements are executed from the top down.

As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the ladder is bypassed. If none of the conditions is true, then the final “else” statement will be executed.

Syntax:

if (condition):

statement

elif (condition):

statement

else:

statement

Example:

In the example, we are showing single if condition, multiple elif conditions, and single else condition.

# Python program to illustrate if-elif-else ladder

#!/usr/bin/python

i = 20