I mentioned Pascal’s Triangle in the previous post, and after typing in the Oz code decided to make a Pascal’s Triangle pretty printer in python.

from sys import argv

def pascal(n):
    if n == 1:
        return [ [1] ]
    else:
        result = pascal(n-1)
        lastRow = result[-1]
        result.append( [ (a+b) for a,b in zip([0]+lastRow, lastRow+[0]) ] )
        return result

def pretty(tree):
    if len(tree) == 0: return ''
    line = '  ' * len(tree)
    for cell in tree[0]:
        line += '  %2i' % cell
    return line + "\n" + pretty(tree[1:])

if __name__ == '__main__':
    print pretty( pascal( int(argv[1]) ) ) 

Which, when run with can generate something like this:

biblio:~/Projects/bookclub ed$ python pascal.py 9
                     1
                   1   1
                 1   2   1
               1   3   3   1
             1   4   6   4   1
           1   5  10  10   5   1
         1   6  15  20  15   6   1
       1   7  21  35  35  21   7   1
     1   8  28  56  70  56  28   8   1 

It’s been fun reading up on the uses for Pascal’s triangle, although I imagine this is old hat for people more familiar with math than I. Still I think getting through this tome will be time well spent in the long run.