MIT的python课的第十七课，一个简单的随机走动模型

[qq_32874397]

import math, random, pylab

class Location(object):

    def __init__(self, x, y):

        self.x = float(x)

        self.y = float(y)

    def move(self, xc, yc):

        return Location(self.x+float(xc), self.y+float(yc))

    def getCoords(self):

        return self.x, self.y

    def getDist(self, other):

        ox, oy = other.getCoords()

        xDist = self.x - ox

        yDist = self.y - oy

        return math.sqrt(xDist**2 + yDist**2)

class CompassPt(object):

    possibles = ('N', 'S', 'E', 'W')

    def __init__(self, pt):

        if pt in self.possibles: self.pt = pt

        else: raise ValueError('in CompassPt.__init__')

    def move(self, dist):

        if self.pt == 'N': return (0, dist)

        elif self.pt == 'S': return (0, -dist)

        elif self.pt == 'E': return (dist, 0)

        elif self.pt == 'W': return (-dist, 0)

        else: raise ValueError('in CompassPt.move')

class Field(object):

    def __init__(self, drunk, loc):

        self.drunk = drunk

        self.loc = loc

    def move(self, cp, dist):

        oldLoc = self.loc

        xc, yc = cp.move(dist)

        self.loc = oldLoc.move(xc, yc)

    def getLoc(self):

        return self.loc

    def getDrunk(self):

        return self.drunk

class Drunk(object):

    def __init__(self, name):

        self.name = name

    def move(self, field, time = 1):

        if field.getDrunk() != self:

            raise ValueError('Drunk.move called with drunk not in field')

        for i in range(time):

            pt = CompassPt(random.choice(CompassPt.possibles))

            field.move(pt, 1)

def performTrial(time, f):

    start = f.getLoc()

    distances = [0.0]

    for t in range(1, time + 1):

        f.getDrunk().move(f)

        newLoc = f.getLoc()

        distance = newLoc.getDist(start)

        distances.append(distance)

    return distances

drunk = Drunk('Homer Simpson')

for i in range(3):

    f = Field(drunk, Location(0, 0))

    distances = performTrial(500, f)

    pylab.plot(distances)
    print distances

pylab.title('Homer\'s Random Walk')

pylab.xlabel('Time')

pylab.ylabel('Distance from Origin')

不太了解第93行的函数是怎么调用的，而且为什么不用继承啊