Python range() Function

The range() function is commonly used with for loops when you want to repeat something a certain number of times or iterate over a sequence of integers.

Basic form — range(n)

Produces integers from 0 up to n - 1. If n is zero or negative, the loop body will not execute.

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

Two parameters — range(a, b)

Produces integers from a up to b - 1. The start is inclusive, the stop is exclusive.

for i in range(2, 7):  # 2, 3, 4, 5, 6
    print(i)

Summing numbers from 1 to n

Use range(1, n+1) to include n in the sequence:

n = 5
total = 0
for i in range(1, n + 1):
    total += i
print(total)  # 15

Three parameters — range(a, b, step)

The third argument sets the step (positive or negative). For example:

• Odd numbers from 1 to 99: range(1, 100, 2)
• Countdown from 100 to 1: range(100, 0, -1)

# Odd numbers
for i in range(1, 100, 2):
    print(i)
Countdown
for i in range(100, 0, -1):
print(i)

Formal definition

In general, for i in range(a, b, step) produces values: i = a, a + step, a + 2*step, … while i < b if step > 0, or i > b if step < 0.

Practical uses

• Repeat an action a fixed number of times
• Iterate over indices of a list
• Create arithmetic progressions
• Work with backwards loops using negative steps

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Key takeaway: range() gives you flexible integer sequences for looping — from simple counters to custom step sizes and reverse iteration.