Outputting a 2^n x 2^n matrix

Question

I've written a simple program in Python which does the following:

Input: an integer \$n\$

Output: a \$2^n x 2^n\$ matrix containing small \$L\$s which fill the entire matrix except one single square. Each L has its unique number, and consists of three squares.

It's a fairly simple program, and you can see clearly what it does by typing in a few different \$n\$s.

What I'd like to do: Keep the actual algorithm as it is now (the rec() function), but improve my C-like code to make full use of Python's features.

#!/usr/bin/env python import sys, math ur = [[1,0], [1,1]] ul = [[0,1], [1,1]] lr = [[1,1], [1,0]] ll = [[1,1], [0,1]] shapeCounter = 1 matrix = [] def printMatrix(): for row in matrix: for element in row: if(element >= 10): print("%d" % element), else: print(" %d" % element), print print def square(n): global matrix matrix = [[0]*(2**n) for x in xrange(2**n)] matrix[0][len(matrix) - 1] = -1 rec(0, 0, len(matrix) - 1, len(matrix) - 1) matrix[0][len(matrix) - 1] = 0 printMatrix() def writeRect(rect, x, y): global shapeCounter matrix[y][x] += rect[0][0] * shapeCounter matrix[y+1][x] += rect[1][0] * shapeCounter matrix[y][x+1] += rect[0][1] * shapeCounter matrix[y+1][x+1] += rect[1][1] * shapeCounter shapeCounter += 1 def rec(sx, sy, ex, ey): if(ex - sx < 1 or ey - sy < 1): return #print("(%d,%d) (%d,%d)" %(sx,sy,ex,ey)) if(matrix[sy][sx] != 0): rect = ul elif(matrix[ey][sx] != 0): rect = ll elif(matrix[sy][ex] != 0): rect = ur elif(matrix[ey][ex] != 0): rect = lr hx = sx + (ex - sx) / 2 hy = sy + (ey - sy) / 2 writeRect(rect, hx, hy) rec(sx, sy, hx, hy) rec(hx + 1, sy, ex, hy) rec(sx, hy + 1, hx, ey) rec(hx + 1, hy + 1, ex, ey) if __name__=='__main__': square(int(sys.argv[1]))

Get out of the habit of using global variables like that. You're just asking for trouble when you do. — Jeff Mercado
– Jeff Mercado, Commented Sep 23, 2012 at 19:19

Winston Ewert · Accepted Answer · 2012-09-23 19:52:36Z

#!/usr/bin/env python import sys, math ur = [[1,0], [1,1]] ul = [[0,1], [1,1]] lr = [[1,1], [1,0]] ll = [[1,1], [0,1]]

Rather then creating four separate variables, I'd suggest making a list. I'd also suggest using the numpy library for its array type. It makes working with 2D arrays much nicer then using lists of lists.

shapeCounter = 1 matrix = []

Don't use global variables. Instead, pass matrix in as the parameter to the function.

def printMatrix(): for row in matrix: for element in row: if(element >= 10):

Parens aren't needed here

 print("%d" % element), else: print(" %d" % element), print print

Note that if you used numpy, that library would already be able to nicely print a matrix.

def square(n): global matrix

This function should really create and return the matrix

 matrix = [[0]*(2**n) for x in xrange(2**n)]

In numpy, this would be matrix = numpy.zeros( (2**n, 2**n) )

 matrix[0][len(matrix) - 1] = -1 rec(0, 0, len(matrix) - 1, len(matrix) - 1) matrix[0][len(matrix) - 1] = 0 printMatrix()

Functions that do work on your variables shouldn't print them. Your main control function should do the printing.

def writeRect(rect, x, y): global shapeCounter

This isn't a terrible use of a global, but I'd avoid it. I'd have an object this attribute was stored on.

 matrix[y][x] += rect[0][0] * shapeCounter matrix[y+1][x] += rect[1][0] * shapeCounter matrix[y][x+1] += rect[0][1] * shapeCounter matrix[y+1][x+1] += rect[1][1] * shapeCounter shapeCounter += 1 def rec(sx, sy, ex, ey):

I wouldn't use abbreviations. Use start_x, end_y to make your code clearer.

 if(ex - sx < 1 or ey - sy < 1): return #print("(%d,%d) (%d,%d)" %(sx,sy,ex,ey)) if(matrix[sy][sx] != 0): rect = ul elif(matrix[ey][sx] != 0): rect = ll elif(matrix[sy][ex] != 0): rect = ur elif(matrix[ey][ex] != 0): rect = lr

You don't need all those parens

 hx = sx + (ex - sx) / 2 hy = sy + (ey - sy) / 2 writeRect(rect, hx, hy) rec(sx, sy, hx, hy) rec(hx + 1, sy, ex, hy) rec(sx, hy + 1, hx, ey) rec(hx + 1, hy + 1, ex, ey) if __name__=='__main__': square(int(sys.argv[1]))

In newer versions of python, print is deprecated as a keyword and requires brackets like any other function. — Aleksandar
– Aleksandar, Commented Sep 24, 2012 at 18:57
@Aleksandar, when I said the parens are unnecessary, I'm referring to the if statement, not print. — Winston Ewert
– Winston Ewert, Commented Sep 24, 2012 at 19:00
Your code view segment shows print, that's what led me to my conclusion. :) — Aleksandar
– Aleksandar, Commented Sep 24, 2012 at 19:02
You'll see that may comments are always after the code they are commenting on, not before. But I might still object to the usage here for being inconsistent. — Winston Ewert
– Winston Ewert, Commented Sep 24, 2012 at 19:04

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