inkdroid

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.

So the Chicago Python Group has started up a bookclub about a month ago. The first book we’re reading as a group is Concepts, Techniques, and Models of Computer Programming which is fortunately available online for free. The aim of the bookclub (as with many bookclubs) is to work through a text together, and hopefully get to hear different perspectives during discussion which will happen online and after our monthly meetings. Also, a bit of peer pressure can help make it through certain types of books…

And this first book is a doozy at 939 pages. It covers all sorts of territory from computer science using a multi-paradigm language called Oz. I’ve made it through the preface, and into Chapter 1, which starts out teaching some fundamental concepts behind functional programming. The jury is still out, but so far I’m finding the content refreshingly clear and stimulating. I like the fact that mathematical notation (so far) is explained and not taken for granted. Calculating factorial with recursion is a bit predictable, but chapter 1 quickly moved on to an algorithm that calculates a given row in a Pascal’s Triangle.

The sheer magnitude of the book is a bit intimdating, however reading it on my ibook makes it easy to ignore that. I’m thinking of it as a sort of thematic encyclopedia of computer programming with handy illustrations. Hopefully I’ll find the time to drop my thoughts here as I work my way through each chapter. Please feel free to join us (whether you’re from Chicago or not) if you are interested.