14. The `range()` function¶

range(start, stop, step)¶

The range() function is used to create a range of numbers in a for loop. It has three parameters with default values, so it can have one, two, or three arguments.

With three arguments:

start is the first integer that the range starts with.

stop is the number that stops the range. It never reaches that value.

step is the value that is added to start to get the consecutive numbers.

Example:
>>> # comenzando en 2, parar en 20, saltando de 3 en 3
>>> list( range(2, 20, 3) )
    [2, 5, 8, 11, 14, 17]

>>> # comenzando en 100, parar en 0, saltando de -10 en -10
>>> list( range(100, 0, -10) )
    [100, 90, 80, 70, 60, 50, 40, 30, 20, 10]

With two arguments:

only the start and stop parameters are used. step is assumed to be equal to one.

Example:
>>> list( range(5, 11) )
    [5, 6, 7, 8, 9, 10]

>>> list( range(-10, 1) )
    [-10, -9, -8, -7, -6, -5, -4, -3, -2, -1, 0]

With an argument:

The argument is copied into the stop parameter.

start is assumed to be zero.

step is assumed equal to one

Example:
>>> list( range(10) )
    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

>>> list( range(2) )
    [0, 1]
Since the range starts at zero, the number of elements in the range is equal to the number we write inside the range function.

Exercises¶

Write a program that prints all even numbers between 2 and 20, inclusive.
Write a program that prints all the odd numbers between 1 and 19, inclusive.
Write a program that prints a countdown that starts by printing 10 and ends by printing 0.
Write a program that writes the following list:
```
50
45
40
35
30
25
20
```
Write a program that writes the following list:
```
-50
-45
-40
-35
-30
-25
-20
```