Another newbie question

[solaris_1234 at yahoo.com]

Mike,

Thanks for your insight. It has been a big help.

I guess I was trying to learn too much with my original code. Trying to
implement inheritance, object creation, calling methods via inheritance
made the code harder than it needed to be.

I'm off to study the code. (Hmm.. how does python parse ("green",
"red")[(i * 8 + j) % 2]  command ... he says while reaching for "python
for the semi-illiterate"  ...)

Again, thanks for your help.


Jpl


Mike Meyer wrote:
> "solaris_1234" <solaris_1234 at yahoo.com> writes:
>
> > 1)  The stmt "board.Blist[10].DrawQueen(board.Blist[10].b1)" seems
> > awkward. Is there another way (cleaner, more intuitive) to get the
> > same thing done?
>
> Yes. Reaching through objects to do things is usually a bad idea. Some
> languages don't allow you to do that at all; they require you to
> provide methods for manipulating the state of the object For instance,
> you can extend your MyBoard class with an extra method:
>
>    def DrawQueen(self, cell):
>        square = self.Blist[cell]
>        square.DrawQueen(square.b1)
>
>
> And then those two lines become:
>
>     board.DrawQueen(10)
>     board.DrawQueen(22)
>
> Except that's still ugly - you probably want something like
> board.DrawQueen(1, 2).
>
> Basically, Blist should be part of MyBoards implementation, not a
> visible attribute. You should define methods for MyBoard that let
> clients manipulate the board, without needing to know how it's
> represented internally.
>
> Along the same lines, why does MyBoard inherit from MyBox? It's not
> using any of the features of MyBox. The code still works if you don't
> do that. And why do you pass instances of Cavnas to the methods of
> MyBox - it's got a canvas already! Do you really expect a MyBox to
> draw onto Canvases other than it's own (if so, that's a bad design as
> well).
>
> Here's an updated version of your code. I've used the convention of an
> _ prefix on attributes to indicate implementation details, and made
> the classes inherit from object, as well as using "box" instead of
> "b1", and changed the interface to MyBoard squares to use standard
> 2d-array indexing instead of forcing the clients to do array
> index calculations. You may have a good reason for doing these things
> that doesn't appear in your code fragment, but I consider these to be
> improvements in the fragment.
>
> Hmm. "b1" seems to indicate that you will eventually have more than
> one canvas, which is why you passed in the canvas? In which case, the
> distinguishing feature would be the number (or mabye the "b1"). In
> that case, have your clients pass in the number (or name), and look up
> the canvas in an internal structure.
>
>     <mike
>
> from Tkinter import *
> import time
> totalSolutionCount = 0
>
> class MyBox(object):
>    def __init__(self, myC, myrow, mycolumn, color):
>       self._box = Canvas(myC, background=color, width=50, height=50)
>       self._box.grid(row=myrow, column=mycolumn)
>       self.occupied = False
>
>    def ChangebgColor(self):
>       self._box.config(bg="black")
>
>    def DrawQueen(self):
>       self._box.item = self._box.create_oval(4,4,50,50,fill="black")
>       self.occupied = True
>       self._box.update()
>
>    def unDrawQueen(self):
>       self._box.delete(self._box.item)
>       self.occupied = False
>       self._box.update()
>
> class MyBoard(object) :
>    def __init__(self, myC):
>       self._blist = {}
>       for i in range(8):
>          for j in range(8):
>              self._blist[i, j] = MyBox(myContainer, i, j,
>                                         ("green", "red")[(i * 8 + j) % 2])
>    def DrawQueen(self, i, j):
>        square = self._blist[i, j]
>        square.DrawQueen()
>
>    def occupied(self, i, j):
>        return self._blist[i, j].occupied
>
>
> root=Tk()
> myContainer = Frame(root)
> myContainer.pack()
>
> board=MyBoard(myContainer)
>
> board.DrawQueen(1, 2)
> board.DrawQueen(2, 6)
>
> raw_input()  # A Hack debug statement
>
> for i in range(8):
>     for j in range(8):
>         if board.occupied(i, j):
>             print "%d, %d is occupied" % (i, j)
>
> raw_input()  # A Hack debug statement
> print "\n"*3
>
>
>
>
> --
> Mike Meyer <mwm at mired.org>			http://www.mired.org/home/mwm/
> Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.