Python range() Function

range() → used to generate a sequence of numbers

range(start, stop, step)

• start → default = 0

• step → default = 1

• stop → not included

examples

range(5)       → 0, 1, 2, 3, 4
range(1, 6)    → 1, 2, 3, 4, 5
range(1, 10, 2) → 1, 3, 5, 7, 9

code examples

for i in range(5):
    print(i)

output

0
1
2
3
4

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

output

1
2
3
4
5

for i in range(1, 10, 2):
    print(i)

output

1
3
5
7
9

Note

• start → where loop begins
• stop → where loop ends (excluded)
• step → increment value
• range() is commonly used with for loop

example (reverse)

for i in range(5, 0, -1):
    print(i)

output

5
4
3
2
1

Question

Write a program in Python to print the sum of first n natural numbers

n = int(input("enter number: "))
 
sum = 0
for i in range(1, n + 1):
    sum += i
 
print("sum =", sum)

output

enter number: 5
sum = 15

Note

• Natural numbers → 1, 2, 3, ... n
• range(1, n+1) → includes n
• sum += i → adds each number to total

• dry run (n = 5)

i	sum
1	1
2	3
3	6
4	10
5	15