All Units Loops

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1. Repeating actions for a range of numbers
   1. Repeating tasks using loops
   2. Changing the loop range
      1. The Range Function

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Repeating actions for a range of numbers

For loops repeat some code for every item in a sequence.

Repeating tasks using loops

The first line of a loop tells the computer how many times the loop will run. Each turn is called an iteration.

The body of the loop is any code that is indented past the loop’s first line. The body gets repeated on each iteration.

In the example below, the variable i is called the loop counter because it keeps track of which iteration we are on.

Code

for i in range(3):
    # This is the body
    print(i)
    # This will print three times

Output

0
1
2

Surprised that the number 3 never printed? Read on.

Changing the loop range

Ranges allow you to specify how many times to run a loop. By default, a range starts at zero. But you can change that!

The Range Function

range(start, stop, [step])

• start: Number to start range at (inclusive), default: 0
• stop: Number to end range before (exclusive)
• step: The gap between each number in the range, default: 1

The range() function returns a value of type range. The range contains numbers between start and stop, but does not include stop.

If only one parameter is given to range(), it will be used as the value for stop.

The range type is different from the list type, but you can convert a range to a list to see what numbers it contains:

numbers = list(range(3, 7))
print(numbers)
# [3, 4, 5, 6]