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Python Loops

Python provides multiple ways to run loops and execute a block of code repeatedly based on a condition or over a sequence. The main types of loops available in Python are the for loop and the while loop, along with nested loops and loop control statements to manage the flow of loops.

Types of Loops

1. While Loop

The while loop repeats a statement or group of statements while a given condition is TRUE. It tests the condition before executing the loop body.

2. For Loop

The for loop executes a code block multiple times and abbreviates the code that manages the loop variable. It is used for iterating over a sequence (such as a list, tuple, dictionary, set, or string).

3. Nested Loops

Nested loops are loops within loops. You can place one loop inside another loop for more complex iteration.

Loop Control Statements

Loop control statements are used to control loops and change the course of iteration. All the objects produced within the local scope of the loop are deleted when execution is completed.

1. Break Statement

The break statement terminates the loop's execution and transfers the program's control to the statement next to the loop.

for i in range(10):
    if i == 5:
        break
    print(i)

2. Continue Statement

The continue statement skips the current iteration of the loop. The statements following the continue statement are not executed once the Python interpreter reaches the continue statement.

for i in range(10):
    if i == 5:
        continue
    print(i)

3. Pass Statement

The pass statement is used when a statement is syntactically necessary, but no code is to be executed.

for i in range(10):
    if i == 5:
        pass
    print(i)

The for Loop

Python's for loop is designed to repeatedly execute a code block while iterating through a list, tuple, dictionary, or other iterable objects of Python. The process of traversing a sequence is known as iteration.

Syntax of the for Loop

sequence = ""
for value in sequence:
#     code block
    pass

# Python program to show how the for loop works

# Creating a sequence which is a tuple of numbers
numbers = [4, 2, 6, 7, 3, 5, 8, 10, 6, 1, 9, 2]

# variable to store the square of the number
square = 0

# Creating an empty list
squares = []

# Creating a for loop
for value in numbers:
    square = value ** 2
    squares.append(square)
print("The list of squares is", squares)

for value in sequence: In this case, the variable value is used to hold the value of every item present in the sequence before the iteration begins until this particular iteration is completed.

Using else Statement with for Loop

The else statement can be used with a for loop. The else block is executed when the loop is exhausted.

# Python program to show how to use else statement with for loop

# Creating a sequence
tuple_ = (3, 4, 6, 8, 9, 2, 3, 8, 9, 7)

# Initiating the loop
for value in tuple_:
    if value % 2 != 0:
        print(value)
# giving an else statement
else:
    print("These are the odd numbers present in the tuple")

The range() Function

With the help of the range() function, we may produce a series of numbers. range(10) will produce values between 0 and 9 (10 numbers).

Parameter Description
start Optional. An integer number specifying at which position to start. Default is 0
stop Required. An integer number specifying at which position to stop (not included).
step Optional. An integer number specifying the incrementation. Default is 1 
# Python program to show the working of range() function
print(range(15))
print(list(range(15)))
print(list(range(4, 9)))
print(list(range(5, 25, 4)))

Using range() in a for Loop

To iterate through a sequence of items, we can apply the range() method in for loops.

while Loop

While loops are used in Python to iterate until a specified condition is met. However, the statement in the program that follows the while loop is executed once the condition changes to false.

Syntax of the while Loop

while condition:
    # Code block to be executed
    # This code block will execute as long as the condition is true

Using else Statement with while Loop

The else statement can be used with the while loop. It has the same syntax as used with the for loop.

Single Statement while Block

The loop can be declared in a single statement, similar to the if-else block.

Detailed Examples of Loop Control Statements

Continue Statement

The continue statement returns the control to the beginning of the loop.

Break Statement

The break statement stops the execution of the loop when the break statement is reached.

Pass Statement

The pass statement is used to create empty loops, classes, functions, and control statements.

Note Loop Control Statements work only inside loop