Python for Loop

Introduction

The for loop in Python is used to iterate over a sequence (such as a list, tuple, string, or range) and execute a block of code for each item in the sequence. The for loop is one of the most commonly used looping constructs in Python due to its simplicity and flexibility.

Syntax

for variable in sequence:
    # block of code

Example

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

Output:

apple
banana
cherry

Using break in a for Loop

The break statement is used to exit the loop prematurely, regardless of the loop condition.

Example

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    if fruit == "banana":
        break
    print(fruit)

Output:

apple

Using continue in a for Loop

The continue statement skips the current iteration and proceeds to the next iteration of the loop.

Example

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    if fruit == "banana":
        continue
    print(fruit)

Output:

apple
cherry

Iterating Over a String

A for loop can be used to iterate over each character in a string.

Example

text = "Hello"
for char in text:
    print(char)

Output:

H
e
l
l
o

The range() Function

The range() function generates a sequence of numbers, which is often used with the for loop to execute a block of code a specific number of times. The range() function has three different ways to be called:

1. range(stop): Generates numbers from 0 to stop - 1.
2. range(start, stop): Generates numbers from start to stop - 1.
3. range(start, stop, step): Generates numbers from start to stop - 1, with a specified step.

Examples

1. Using range(stop):

   for i in range(5):
       print(i)
   

   Output:

   0
   1
   2
   3
   4
   

2. Using range(start, stop):

   for i in range(2, 7):
       print(i)
   

   Output:

   2
   3
   4
   5
   6
   

3. Using range(start, stop, step):

   for i in range(1, 10, 2):
       print(i)
   

   Output:

   1
   3
   5
   7
   9
   

Simple Programs Using for Loop

Program 1: Sum of First N Natural Numbers

This program calculates the sum of the first n natural numbers.

n = 10
sum = 0

for i in range(1, n + 1):
    sum += i

print(f"The sum of the first {n} natural numbers is {sum}")

Output:

The sum of the first 10 natural numbers is 55

Program 2: Factorial of a Number

This program calculates the factorial of a given number.

num = 5
factorial = 1

for i in range(1, num + 1):
    factorial *= i

print(f"The factorial of {num} is {factorial}")

Output:

The factorial of 5 is 120

Program 3: Print Each Character of a String

This program prints each character of a given string.

text = "Hello, World!"

for char in text:
    print(char)

Output:

H
e
l
l
o
,

W
o
r
l
d
!

Program 4: Iterate Over a List of Numbers and Print Their Squares

This program iterates over a list of numbers and prints their squares.

numbers = [1, 2, 3, 4, 5]

for num in numbers:
    print(f"The square of {num} is {num**2}")

Output:

The square of 1 is 1
The square of 2 is 4
The square of 3 is 9
The square of 4 is 16
The square of 5 is 25

Program 5: Print Even Numbers from a List

This program prints all the even numbers from a given list.

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

for num in numbers:
    if num % 2 == 0:
        print(f"{num} is an even number")

Output:

2 is an even number
4 is an even number
6 is an even number
8 is an even number
10 is an even number

Conclusion

The for loop in Python is used for iterating over sequences and performing repetitive tasks efficiently. By understanding how to use the for loop, along with the range() function and control statements like break and continue, you can write more flexible and efficient code. The provided examples and programs demonstrate practical applications of the for loop in solving common programming tasks.