Python Loops and Control Structures

Python Loops and Control Structures

Python provides several loop structures and control statements to manipulate the flow of execution in a program. In this article, we will explore the basics of Python loops and control structures, focusing on the subtopics of while loops, for loops, if statements, else statements, and elif statements.

While Loops

A while loop is a conditional loop that continues to execute as long as a certain condition is met. The general syntax of a while loop is:

while expression:
    statements

In this loop, the expression is evaluated before each iteration. If the expression is true, the statements within the loop are executed. If the expression becomes false, the loop terminates.

For example, consider the following while loop that prints numbers from 1 to 5:

i = 1
while i <= 5:
    print(i)
    i += 1

In this code, the loop iterates 5 times, printing the value of i on each iteration. After the loop terminates, i is incremented by 1 to prepare for the next iteration.

For Loops

A for loop is another type of loop in Python that allows you to iterate over a sequence of elements. The general syntax of a for loop is:

for variable in sequence:
    statements

In this loop, variable is assigned the value of each element in the sequence during each iteration. The statements within the loop are then executed.

For example, consider the following for loop that prints each letter in the string "Python":

for letter in 'Python':
    print(letter)

In this code, the loop iterates 5 times, assigning the value of each letter to letter and then printing it.

If Statements

An if statement is used to execute a block of code only if a certain condition is met. The general syntax of an if statement is:

if expression:
    statements

In this statement, the expression is evaluated. If the expression is true, the statements within the if block are executed.

For example, consider the following if statement that checks if a number is even and prints "Even" if it is:

number = 2
if number % 2 == 0:
    print("Even")

In this code, the if statement checks if number is divisible by 2 with no remainder. If it is, the message "Even" is printed.

Else Statements

An else statement is used to execute a block of code when the condition in an if statement is not met. The general syntax of an else statement is:

if expression:
    statements
else:
    statements

In this statement, the expression is evaluated. If the expression is true, the statements within the if block are executed. If the expression is false, the statements within the else block are executed.

For example, consider the following code that uses an if and an else statement to check if a number is even or odd:

number = 3
if number % 2 == 0:
    print("Even")
else:
    print("Odd")

In this code, the if statement checks if number is divisible by 2 with no remainder. If it is, the message "Even" is printed. If it is not, the message "Odd" is printed.

Elif Statements

An elif statement is used to specify multiple conditions for an if statement, allowing you to handle multiple scenarios. The general syntax of an elif statement is:

if expression1:
    statements1
elif expression2:
    statements2
...
else:
    statements

In this statement, the expression1 is evaluated. If it is true, the statements1 within the if block are executed. If expression1 is false, the expression2 is evaluated. If it is true, the statements2 within the elif block are executed. This process continues until an if or an elif condition is met, or until the else block is executed if none of the conditions are met.

For example, consider the following code that uses an if and multiple elif statements to check if a number is even, odd, or prime:

number = 5
if number % 2 == 0:
    print("Even")
elif number % 3 == 0:
    print("Odd")
elif number % 5 == 0:
    print("Prime")
else:
    print("Not prime")

In this code, the if statement checks if number is divisible by 2 with no remainder. If it is, the message "Even" is printed. If it is not, the elif statement checks if number is divisible by 3 with no remainder. If it is, the message "Odd" is printed. If it is not, the elif statement checks if number is divisible by 5 with no remainder. If it is, the message "Prime" is printed. If none of these conditions are met, the else block is executed, and the message "Not prime" is printed.

In conclusion, Python provides various loop structures and control statements to manipulate the flow of execution in a program. Understanding and using these structures effectively is essential for writing efficient and well-structured code.

Explore the basics of Python loops and control structures, including while loops, for loops, if statements, else statements, and elif statements. Learn how to use these structures effectively to manipulate the flow of execution in a program.