Point.py

import math

EPSILON=1e-20 # for testing equality of real numbers

class UnderDetermined(Exception): 
 """
 Raised in case of non-uniqueness of result
 """
 pass

class Point:
 """
 Encapsulates the essence of a point in 2D cartesian space
 """

 def __init__(self, x=0, y=0):
  """
  Point constructor.
  Set x and y coordinates (both default to 0)
  """
  self.set_x(x)
  self.set_y(y)

 def set_x(self, x=0):
  """
  Set the private attribute x 
  """
  self.__x = x

 def set_y(self, y=0):
  """
  Set the private attribute y 
  """
  self.__y = y

 def get_x(self):
  """
  Get the private attribute x 
  """
  return self.__x

 def get_y(self):
  """
  Get the private attribute y 
  """
  return self.__y

 def get_r(self):
  """
  Get the polar coordinate radius 
  """
  x=self.get_x() 
  y=self.get_y() 
  return(math.sqrt(x*x+y*y))

 def get_theta(self):
  """
  Get the polar coordinate theta 
  """
  x=self.get_x()
  y=self.get_y()
  if math.fabs(x) < EPSILON:
   if math.fabs(y) < EPSILON:
    raise UnderDetermined, "infinitely many theta values possible" 
   elif y > 0:
     theta = math.pi/2
   else:
     theta = -math.pi/2
  else:
   theta=math.atan(y/x)
  return theta

 def translate(self, delta_x, delta_y):
  """
  Translate self over delta_x, delta_y 
  """
  self.set_x(self.get_x()+delta_x)
  self.set_y(self.get_y()+delta_y)

 def rotate(self, angle):
  """
  Rotate self over angle 
  """
  r=self.get_r()
  theta=self.get_theta()+angle
  self.set_x(r*math.cos(theta))
  self.set_y(r*math.sin(theta))

 def __str__(self):
  """
  String representation of self
  """
  return("Point("+str(self.get_x())+","+str(self.get_y())+")")

 def __eq__(self, other):
  """
  Test for equality (==)
  """
  diff_x = math.fabs(self.get_x() - other.get_x())
  diff_y = math.fabs(self.get_y() - other.get_y())
  if diff_x < EPSILON and diff_y < EPSILON: 
   return True
  else:
   return False