LM FOR Loop in range()

What are For-Loops?

For-loops are a core structure in Python that repeat a block of code multiple times. They are ideal when the number of repetitions is known in advance. In Python, the most common way to repeat something a fixed number of times is by using the range() function.

▶ Basic Example

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

Output:

0
1
2
3
4

You can use range(start, stop) to repeat something from a starting number up to, but not including, a stopping number:

for i in range(7, 11):
    print(i)

Output:

7
8
9
10

range(7, 11) includes 7 but excludes 11.

The variable i is updated automatically in each step. You should not change it inside the loop body.

Stepping Through the Range

You can also define a step size with range(start, stop, step).

Example 1: Every second number

for i in range(0, 10, 2):
    print(i)

Output:

0
2
4
6
8

Example 2: Check for even numbers

for i in range(6):
    if i % 2 == 0:
        print(i, "is even")

This loop checks each number from 0 through 5 and prints the even numbers.

Counting Down

If you want to count backwards, use a negative step:

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

Output:

5
4
3
2
1

Make sure that the start is greater than the stop when using a negative step.

Summary

  • range(n) loops from 0 to n-1.
  • range(start, stop) loops from start to stop - 1.
  • range(start, stop, step) controls how much the number increases (or decreases).
  • You can loop forwards or backwards using range().

These loops are very useful when you want to do something a specific number of times or when working with positions like indexes in a list.

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