The Range Function

The range() function in Python generates a sequence of numbers, which is commonly used with for loops to repeat code a specific number of times.

Create a range that starts at 0 and ends at 4:

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

This will output:

0
1
2
3
4

You can also specify a start value:

for i in range(2, 6):
    print(i)

This will output:

2
3
4
5

And you can specify a step value (increment):

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

This will output:

1
3
5
7
9

Counting Backwards (Descending Order):

You can also use a negative step value to count backwards. When using a negative step, the start value must be greater than the end value:

for i in range(10, 0, -1):
    print(i)

This will output:

10
9
8
7
6
5
4
3
2
1

You can also use larger negative steps:

for i in range(20, 9, -2):
    print(i)

This will output:

20
18
16
14
12
10

Notice that 10 is included in the output even though the end value is 9. This is because the end value is exclusive — the loop continues as long as the current value is greater than the end value. Since 10 > 9, it is printed. The next step would be 8, which is not greater than 9, so the loop stops.

Key Point: When using a negative step, the start value must be greater than the end value. The end value is still exclusive (not included).