Help understanding the decisions *behind* python?

[Inky 788]

On Jul 23, 3:42 am, Hendrik van Rooyen <hend... at microcorp.co.za>
wrote:
> On Wednesday 22 July 2009 16:36:51 Inky 788 wrote:
>
> > On Jul 22, 2:36 am, Hendrik van Rooyen <hend... at microcorp.co.za>
>
> > wrote:
> > > The good reason is the immutability, which lets you use
> > > a tuple as a dict key.  
>
> > Thanks for the reply Hendrik (and Steven (other reply)). Perhaps I'm
> > just not sophisticated enough, but I've never wanted to use a list/
> > tuple as a dict key. This sounds like obscure usage, and a bit
> > contrived as a reason for having *both* lists and tuples.
>
> Steven showed why you cannot have a mutable thing
> as a key in a dict.
>
> if you think it is contrived, then please consider how you would
> keep track of say the colour of a pixel on a screen at position
> (x,y) - this is about the simplest "natural" tuple format and
> example.

My guess is that this is probably the way most people do it:

~~~~
#!/usr/bin/env python

import sys
import random

if len( sys.argv ) != 3:
    print "Please pass exactly 2 ints. Exiting."
    sys.exit(1)

NUM_COLUMNS = int( sys.argv[1] )
NUM_ROWS    = int( sys.argv[2] )

print "Making array of %s columns by %s rows." % (NUM_COLUMNS,
NUM_ROWS)

def rand():
    return int( 255 * random.random())

def make_a_pixel():
    #       red     green   blue
    return [rand(), rand(), rand()]

def make_a_row(num_columns):
    temp_row = []
    for i in range(num_columns):
        temp_row.append( make_a_pixel() )
    return temp_row

def make_array_of_pixels(num_columns, num_rows):
    rows = []
    for i in range(num_rows):
        rows.append( make_a_row(num_columns) )
    return rows

def show_pixels(pixel_array):
    for row in pixel_array:
        for pixel in row:
            print pixel, '  ',
        print


rows_of_pixels = make_array_of_pixels(NUM_COLUMNS, NUM_ROWS)

show_pixels(rows_of_pixels)
~~~~