Loops in Python

Loops allow you to execute a block of code repeatedly. Python provides two main types: for and while loops.

For Loops

The for loop iterates over a sequence (list, tuple, string, range, etc.):

# Iterating over a list
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

# Using range()
for i in range(5):
    print(i)  # 0, 1, 2, 3, 4

# Iterating with index
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")

While Loops

The while loop continues as long as the condition is true:

count = 0
while count < 5:
    print(count)
    count += 1

Loop Control Statements

break

Exits the loop immediately:

for i in range(10):
    if i == 5:
        break
    print(i)  # Prints 0-4

continue

Skips the rest of the current iteration:

for i in range(10):
    if i % 2 == 0:
        continue
    print(i)  # Prints odd numbers

else Clause

The else block runs when the loop completes without break:

for item in items:
    if item == target:
        print("Found!")
        break
else:
    print("Not found")

List Comprehensions

A concise way to create lists using loops:

# Traditional approach
squares = []
for x in range(10):
    squares.append(x ** 2)

# List comprehension
squares = [x ** 2 for x in range(10)]

# With condition
evens = [x for x in range(20) if x % 2 == 0]

Advanced Patterns

Nested Loops

matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
for row in matrix:
    for cell in row:
        print(cell, end=" ")
    print()

zip() for Parallel Iteration

names = ["Alice", "Bob"]
ages = [30, 25]
for name, age in zip(names, ages):
    print(f"{name} is {age}")