Christmas tree --- nested while loop example

Script

#!/usr/local/bin/python3.1

blanks = 20
stars = 1
line = 0

while line < 18:
        i = 0
        j = 0
        while i < blanks:
                print('', end=' '),
                i = i + 1
        print()
        while j < stars:
                print("*", end=' ')
                j = j + 1

        stars = stars + 2
        line = line + 1
print()

Execution

*

* * *

* * * * *

* * * * * * *

* * * * * * * * *

* * * * * * * * * * *

* * * * * * * * * * * * *

* * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *