#!/usr/env python

#====================================================================

class Polygon:
	'''General Polygon class'''
	verticies = []
	def __init__ (self, verts = None):
		''' init for Poly!'''
		for x in verts:
			try:
				if len(x) >= 2:
					#print x[0], x[1]
					self.verticies.append((int(x[0]),int(x[1])))
						
			except TypeError, ValueError:
				print "Incorrect"
				
		
#______________________________________________________________________
		
	def perimeter(self):
		p = 0.0
		v = self.verticies
		for i in range(len(v)):
			offs = -len(v)+i+1
			p += sum([(v[offs][y] - v[offs+1][y])**2 for y in range(2)])**0.5
			
		return p
					
#______________________________________________________________________

	def area (self):
		area = 0.0
		for i in range (1, len(self.verticies)-1):
			area += self.areaTriangle(0,i,i+1)
		return area
		
		
#______________________________________________________________________
	
	def areaTriangle (self, a,b,c):
		l = []
		v = [a,b,c]
		try:
			l = [list(self.verticies[int(x)]) for x in v]
		except ValueError:
			return
		
		det = 0.0
		for i in range(3):
			det += (l[-3+i][0]*(l[-1+i][1]-l[-2+i][1]))*((-1)**i)
		return abs(det/2)
				
#====================================================================

##-Ignore this----------------------------------------------
class Rectangle (Polygon):
	def __init__ (self, dim = (0,0,0,0)):
		try:
			for i in ((0,1),(2,0), (2,3), (0,3)):
				print i
				self.verticies.append((int(dim[i[0]]),int(dim[i[1]])))
		except ValueError:
			self.verticies = []
			
	#def area():
	#	pass

##------------------------------------------------------------


##====main===================================================
if __name__ == "__main__":
	
	f = Polygon([(0,0), (3,0), (3,3), (0,3)])
	print f.verticies
	g = Polygon([(0,0), (3,0), (3,3), (0,3)])
	print g.verticies
	g.verticies[0] = (9,9)
	print
	print f.verticies
	print g.verticies
	print "areatri = "+  str(f.areaTriangle(0,1,2))
	print f.area()
	
	print f.perimeter()
	
	#r = Rectangle((0,0,4,4))
	#r2 = Rectangle((0,0,5,5))
	
	#print r2.verticies