Python Class / Instance /Object Organization Question

Question

The following is a simplified example for something I'm trying to do in python (with pygame, but that's probably irrelevant).

I have a list of 8x8 pixel jpgs, each depicting an English letter:

[a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z]

I want to arrange a 4x4 grid of these, in any pattern I want, as a larger 32x32 picture:

gmmg
gppg
gppg
gmmg

But that pattern is only a single frame of an animation. For example, I might want 4 animation frames where b's and n's flash side to side alternately while an f moves southwest:

bbnf nnbb bbnn nnbb
bbnn nnfb bbnn nnbb
bbnn nnbb bfnn nnbb
bbnn nnbb bbnn fnbb

I want control over the letter value of each square in each frame to make any animation, so I guess essentially there are 64 separate variables (for a 4-frame animation like the one shown above). Each square also has an [x,y] list position variable and rbg color.

My question is how to organize this all with classes (I'm trying to learn OOP). Logically, it seems that each frame contains squares, and each square contains variables like position, letter and color. But I suppose you could even think of it as each square 'contains' 4 frames... My guess is make a frame class, and put 4 instances of it in a list (if there's 4 frames) and somehow make each frame instance contain a list of 16 square instances. Maybe usable like frames[2].squares[5].letter = f (Just a fuzzy idea; I'm too new at OOP to know if that's remotely correct or a good idea). But it would be helpful to see how someone who knows what they're doing would organize all this. Thanks!

Quick tip, for a 4x4 grid, use a list of lists. So you can do squares[3][0], rather than squares[8]. — Thomas K
– Thomas K, Commented Feb 6, 2011 at 17:42

Mike DeSimone · Accepted Answer · 2011-02-06 22:11:32Z

Since the size of a frame is fixed, and the number of frames is not, then making a class Frame seems like a good first choice. Each Frame would contain a member grid which could be a list of four lists of four letters. A list of four strings wouldn't work as well since strings are immutable, though having it be a single 16-character string might perform better. You'd have to profile to be sure. For this answer, I'll assume you're going with a list of lists of characters.

Then make a class Animation that has a frames member, which is a list of frames. Then you'll write code that looks like:

myAnimation.frames[10].grid[2][3] = 'f'

I can provide more detail if desired.

EXAMPLE: (Haven't tested this yet, but it should be close. The doc comments should hopefully work with doctest.)

import string

class Frame(object):
    """This is a single frame in an animation."""
    def __init__(self, fill=None, color=None):
        """Initializes the frame.

        >>> f = Frame()
        >>> f.print()
        aaaa
        aaaa
        aaaa
        aaaa
        >>> g = Frame(fill='c', color=(0, 255, 0))
        >>> g.print()
        cccc
        cccc
        cccc
        cccc
        """
        if fill is None:
            fill = 'a' # Or whatever default you want
        self.letterGrid = []
        for row in range(4):
            self.letterGrid.append([fill for col in range(4)])

        if color is None:
            color = (0, 0, 0)
        self.colorGrid = []
        for row in range(4):
            self.letterGrid.append([fill for col in range(4)])

    def set_grid(self, row, col, letter=None, color=None):
        """Sets the letter and/or color at the given grid.

        >>> f.set_grid(1, 1, 'b', (255, 0, 0))
        >>> f.print()
        aaaa
        abaa
        aaaa
        aaaa
        >>> f.set_grid(1, 3, letter='x')
        >>> f.print()
        aaaa
        abax
        aaaa
        aaaa
        >>> f.set_grid(3, 3, color=(255, 0, 0))
        """
        if letter is not None:
            self.letterGrid[row][col] = letter
        if color is not None:
            self.colorGrid[row][col] = color

    def position(row, col):
        return (row * 16, col * 16)

    def print(self):
        """Simple routine to print a frame as text."""
        for row in self.letterGrid:
            print(''.join(row))

class Animation(object):
    def __init__(self, frames=None):
        """Initializes an animation."""
        self.frames = frames or []

Hope this gets you started.

I desire :) I posted my attempt at the Frame class below. Not sure if its good and seeing your pseudo code or something would probably help me learn a lot faster than googling, if you can be bothered.

flow · Accepted Answer · 2011-02-06 19:09:31Z

0

the alternative approach would be to come up with a suitable generic datastructure solely made up from dictionaries, lists, sets and so on, and then write library methods to manipulate that data. that doesn't sound very classical OOP, and it isn't, but i've found that way easier to handle and easier to 'get right'. you can clearly seperate the two concerns of building data containers on the one hand and defining suitable data manipulation code on the other.

as earlier posters suggested, the animation could be modeled as a list of frames; each frame then either contains 32 lists with 32 elements each, or 8 lists with 8 elements each where each element models again the 4x4 grid shown above. of course, whether you actually precompute (or simply define) each frame beforehand, or whether you manipulate the data of a single frame 'live' during the animation depends on further considerations.

answered Feb 6, 2011 at 19:09

flow

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1 Comment

cheeser Over a year ago

I used to pretty much only use lists but am trying to learn OOP to see if I can organize stuff better and make it human-understandable. Lists could often work but took me a long time to think through, and my ability to control stuff was limited to low complexity. I might have done it wrong but I'd often end up with very nested lists that are confusing to loop through and numbers such as myList[3][5][8] or something isn't very human readable.

cheeser · Accepted Answer · 2011-02-06 20:29:33Z

@Mike (replying to you above was limited to 600 characters so I guess I'll show my reply here) This is my attempt at the Frame class so far. I don't know if I should define one class inside another or whether or how to send a list of instances to the Animation class or something. Each square can have a unique letter, position, and color (position because I intend for the columns or rows to be positionally shiftable). So that's why I put 3 types of grids in there (not sure if that's a good idea, or whether an individual square should have its own class too or something).

class Frame(object):
    def __init__(self, letterGrid, positionGrid, colorGrid):
        self.letterGrid = letterGrid
        self.positionGrid = positionGrid
        self.colorGrid = colorGrid

class Animation(object):
    def __init__(self, frames):
        self.frames = frames

frames = []
frames.append(Frame( [
                    ['b','b','n','f'],
                    ['b','b','n','n'],
                    ['b','b','n','n'],
                    ['b','b','n','n'] ],

                    [
                    [[0,0],[16,0],[32,0],[48,0]],
                    [[0,16],[16,16],[32,16],[48,16]],
                    [[0,32],[16,32],[32,32],[48,32]],
                    [[0,48],[16,48],[32,48],[48,48]] ],

                    [
                    [[0,0,255],[0,0,0],[0,0,0],[0,0,0]],
                    [[0,0,255],[0,0,0],[0,0,0],[0,0,0]],
                    [[0,0,255],[0,0,0],[0,0,0],[0,0,0]],
                    [[0,0,255],[0,0,0],[0,0,0],[0,0,0]] ]
                    ))

frames.append(Frame( [
                    ['n','n','b','b'],
                    ['n','n','f','b'],
                    ['n','n','b','b'],
                    ['n','n','b','b'] ],

                    [
                    [[0,0],[16,0],[32,0],[48,0]],
                    [[0,16],[16,16],[32,16],[48,16]],
                    [[0,32],[16,32],[32,32],[48,32]],
                    [[0,48],[16,48],[32,48],[48,48]] ],

                    [
                    [[0,0,0],[0,0,255],[0,0,0],[0,0,0]],
                    [[0,0,0],[0,0,255],[0,0,0],[0,0,0]],
                    [[0,0,0],[0,0,255],[0,0,0],[0,0,0]],
                    [[0,0,0],[0,0,255],[0,0,0],[0,0,0]] ]
                    ))

frames.append(Frame( [
                    ['b','b','n','n'],
                    ['b','b','n','n'],
                    ['b','f','n','n'],
                    ['b','b','n','n'] ],

                    [
                    [[0,0],[16,0],[32,0],[48,0]],
                    [[0,16],[16,16],[32,16],[48,16]],
                    [[0,32],[16,32],[32,32],[48,32]],
                    [[0,48],[16,48],[32,48],[48,48]] ],

                    [
                    [[0,0,0],[0,0,0],[0,0,255],[0,0,0]],
                    [[0,0,0],[0,0,0],[0,0,255],[0,0,0]],
                    [[0,0,0],[0,0,0],[0,0,255],[0,0,0]],
                    [[0,0,0],[0,0,0],[0,0,255],[0,0,0]] ]
                    ))

frames.append(Frame( [
                    ['n','n','b','b'],
                    ['n','n','b','b'],
                    ['n','n','b','b'],
                    ['n','n','b','b'] ],

                    [
                    [[0,0],[16,0],[32,0],[48,0]],
                    [[0,16],[16,16],[32,16],[48,16]],
                    [[0,32],[16,32],[32,32],[48,32]],
                    [[0,48],[16,48],[32,48],[48,48]] ],

                    [
                    [[0,0,0],[0,0,0],[0,0,0],[0,0,255]],
                    [[0,0,0],[0,0,0],[0,0,0],[0,0,255]],
                    [[0,0,0],[0,0,0],[0,0,0],[0,0,255]],
                    [[0,0,0],[0,0,0],[0,0,0],[0,0,255]] ]
                    ))

print "3rd frame's colorGrid:\n", frames[2].colorGrid

You don't need positionGrid; it is constant and can be computed as needed, right? So just have a method def position(row, col): return (row * 16, col * 16)

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