Loops in Python

Introduction to Loops

In programming, loops are used to execute a block of code repeatedly without writing the same code multiple times. This is especially useful when dealing with large datasets or repetitive tasks.

Real-World Analogy

Imagine you want to print numbers from 1 to 100. Writing 100 print statements is inefficient. A loop allows you to achieve this with just a few lines of code.

Types of Loops

• for loop: Used when the number of iterations is known
• while loop: Used when the number of iterations depends on a condition

Example

for i in range(1, 6):
    print(i)

Key Concepts

• Iteration: One complete execution of the loop body
• Loop control variable: Tracks the progress of the loop
• Condition: Determines when the loop stops

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• for Loop

The for loop is used to iterate over a sequence such as a list, tuple, string, or range.

Syntax

for variable in sequence:
    # code block

Example with range()

for i in range(1, 6):

print(i)

//Understanding range()

range(5) → 0 to 4

range(1, 6) → 1 to 5

range(1, 10, 2) → 1, 3, 5, 7, 9

//Iterating Over Different Data Types

//List Example

numbers = [10, 20, 30]
for num in numbers:
    print(num)

//String Example

for char in "Python":
    print(char)

//Using else with for Loop

for i in range(3):
    print(i)
else:
    print("Loop finished")

Key Points

• Automatically iterates over elements
• No need for manual counter management
• Widely used for traversing collections

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• while Loop

The while loop executes as long as a condition remains true.

Syntax

while condition:
    # code block

Example

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

//Infinite Loop

while True:
    print("This runs forever")

//Using else with while

i = 1
while i <= 3:
    print(i)
    i += 1
else:
    print("Loop ended")

Important Notes

• Condition must eventually become False
• Forgetting to update variables leads to infinite loops

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• break Statement

The break statement is used to terminate a loop immediately when a condition is met.

Example

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

Explanation

• Loop stops when i == 5
• Remaining iterations are skipped

Use Cases

• Searching for an element
• Exiting loops early for efficiency

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• continue Statement

The continue statement skips the current iteration and moves to the next one.

Example

for i in range(5):
    if i == 2:
        continue
    print(i)

Explanation

• When i == 2, the loop skips printing
• Continues with next iteration

Use Cases

• Skipping unwanted values
• Filtering data

---

• pass Statement

The pass statement acts as a placeholder. It does nothing but prevents syntax errors when a statement is required.

Example

for i in range(5):
    if i == 3:
        pass
    print(i)

When to Use

• While writing incomplete code
• Creating empty loops or functions

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• Nested Loops

Nested loops are loops inside another loop. They are useful for working with multi-dimensional data or creating patterns.

Syntax

for i in range(3):
    for j in range(3):
        print(i, j)

Example (Multiplication Table)

for i in range(1, 4):
    for j in range(1, 4):
        print(i * j, end=" ")
    print()

//Pattern Example

for i in range(4):
    for j in range(i + 1):
        print("*", end=" ")
    print()

Output

*
* *
* * *
* * * *

Key Points

• Inner loop runs completely for each outer loop iteration
• Can increase complexity
• Should be used carefully to maintain readability

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Conclusion

Loops are a fundamental concept in Python that allow repetitive tasks to be handled efficiently. The for loop is ideal for iterating over sequences, while the while loop is useful when repetition depends on conditions. Control statements like break, continue, and pass provide flexibility in managing loop behavior.

By mastering loops, learners can solve complex problems, process large datasets, and write optimized programs. This knowledge forms a strong foundation for advanced topics such as data structures, algorithms, and real-world application development.