Loops: for and while

Loops let you repeat a block of code multiple times. Python has two loop constructs: for loops (for iterating over sequences) and while loops (for repeating while a condition is true). Mastering loops is essential — they are one of the most powerful tools in programming.

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The for Loop

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

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

# Loop through a string
for char in "Python":
    print(char, end=" ")
# P y t h o n

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The range() Function

range() generates a sequence of numbers — perfect for loops:

# range(stop) — 0 to stop-1
for i in range(5):
    print(i, end=" ")
# 0 1 2 3 4

# range(start, stop)
for i in range(2, 6):
    print(i, end=" ")
# 2 3 4 5

# range(start, stop, step)
for i in range(0, 20, 3):
    print(i, end=" ")
# 0 3 6 9 12 15 18