"""
We want an array, but not just any old array, an array with
contents!

Write a function that produces an array with the numbers 0
to N-1 in it.

For example, the following code will result in an array
containing the numbers 0 to 4:

arr(5) // => [0,1,2,3,4]
Note: The parameter is optional. So you have to give it
a default value.
"""

def arr(n = 0): 
    return [x for x in range(n)]

print('Tests:')
print(arr(4))
print(arr(0))
print(arr())