[Edu-sig] Design patterns

[Kirby Urner]

> -----Original Message-----
> From: edu-sig-bounces+urnerk=qwest.net at python.org [mailto:edu-sig-
> bounces+urnerk=qwest.net at python.org] On Behalf Of Chuck Allison
> Sent: Tuesday, August 23, 2005 6:19 PM
> To: Kirby Urner
> Cc: edu-sig at python.org
> Subject: Re: [Edu-sig] Design patterns
> 
> Hello Kirby,
> 
> Thanks for this good input (you too, Scott). My syllabus is at
> http://uvsc.freshsources.com/html/cns_439r.html. I like your point
> about cutesy having its place. I just don't see a way to use what's in
> HFDP as the basis for a programming assignment, but maybe it will come
> after a few days. As a professor, I like having my ducks in a row a
> priori, but that's not happening this first time around. Since I teach
> 3 upper division courses, I'm just a little nervous about having time
> to invent sufficient material. I was just hoping someone had had a
> similar teaching experience I could "borrow" from. All comments
> appreciated. Thanks again.

Hi Chuck --

I don't have HFDP in front if me, but if it does MVC at all, I can imagine
using the Triangle we've been discussing as a model, then adding viewer and
controller objects, making the triangle change in some way (controlling it),
while displaying (viewing it).

Here's some code, which as yet doesn't actually make use of VPython -- but
that's where it's going.  

Note that my viewer expects to work with a 'shape' object, which is supposed
to have attributes verts (a dictionary of labeled vertices) and edges (a
list of vertex pairs, using those labels).  Since my triangle object wasn't
written that way, I subclass a Triangle2 as TriAdapter, solely for the
purpose of making it behave like a shape.

Kirby

===
# uses code already/recently posted to this list for BaseTriangle

class Triangle2(BaseTriangle):
    """
    Model
    """

    @property
    def coords(self):
        return {'A':self._pA, 'B':self._pB, 'C':self._pC}

    def _reset(self):
        a,b,c = self.a, self.b, self.c # for brevity
        self.perimeter = a + b + c
        s = 0.5 * self.perimeter
        self.area = math.sqrt(s * (s - a)*(s - b)*(s - c))
        self.A = math.acos((-a**2 + b**2 + c**2)/(2.0*b*c))
        self.B = math.acos(( a**2 - b**2 + c**2)/(2.0*a*c))
        self.C = math.acos(( a**2 + b**2 - c**2)/(2.0*a*b))         
        self._pA = (0.0, 0.0, 0.0)
        self._pB = (a  , 0.0, 0.0)
        self._pC = ((a**2 + b**2 - c**2)/(2.0*a),
                     math.sqrt((-a+b+c)*(a-b+c)*(a+b-c)*(a+b+c))/(2*a),
                     0.0)         

    def __mul__(self, scalar):
        a = self.a * scalar
        b = self.b * scalar
        c = self.c * scalar
        return self.__class__(a,b,c)     

    __rmul__ = __mul__


class TriAdapter(Triangle2):
    """
    Make a triangle work like a Shape, i.e. add
    edges and verts attributes
    """

    def __init__(self, a,b,c):
        Triangle2.__init__(self, a,b,c)
        self.edges = [('A','B'),('B','C'),('C','A')]
        
    @property
    def verts(self):
        return self.coords
        
class Pulser(object):
    """
    A controller:  makes a shape bigger in steps, 
    then smaller, back to original    
    """

    def __init__(self, shape, viewer):
        self.shape = shape
        self.viewer = viewer
        
    def run(self):
        for i in range(15):
            self.viewer.display(self.shape)
            self.shape = self.shape * 1.1
        for i in range(16):
            self.viewer.display(self.shape)
            self.shape = self.shape * (1/1.1)

class Vpyview(object):
    """
    A viewer: view using VPython -- very unfinished
    """
    
    def display(self, shape):
        self._showverts(shape.verts)
        self._showedges(shape.edges)

    def _showedges(self, edges):
        # stub method
        for e in edges:
            print e
            
    def _showverts(self, verts):
        # stub method        
        for v in verts:
            print v, verts[v]
    
def main():
    """
    Main call sequence -- maybe loop through random 
    triangles eventually
    """
    theviewer = Vpyview()    
    theshape = TriAdapter(3,3,3)  
    pulser = Pulser(theshape, theviewer)
    pulser.run()