CSP.py

# CLASS DESCRIPTION FOR CSP

from helper import *

class csp:
	
	#INITIALIZING THE CSP
	def __init__ (self, domain = digits, grid = ""):
		self.variables = squares
		self.domain = self.getDict(grid)
		self.values = self.getDict(grid)
		self.VARconstraints = []


		'''
			Unitlist consists of the 27 lists of peers 
			Units is a dictionary consisting of the keys and the corresponding lists of peers 
			Peers is a dictionary consisting of the 81 keys and the corresponding set of 20 peers 
			Constraints denote the various all-different constraints between the variables 
		'''

		self.unitlist = ([cross(rows, c) for c in cols] +
            			 [cross(r, cols) for r in rows] +
            			 [cross(rs, cs) for rs in ('ABC','DEF','GHI') for cs in ('123','456','789')])

		self.units = dict((s, [u for u in self.unitlist if s in u]) for s in squares)
		self.peers = dict((s, set(sum(self.units[s],[]))-set([s])) for s in squares)
		self.constraints = list({(variable, peer) for variable in self.variables for peer in self.peers[variable]})
		#self.constraints2 = list({(variable, peer) for variable in self.variables for peer in self.peers[variable]})
                        
	#GETTING THE STRING AS INPUT AND RETURNING THE CORRESPONDING DICTIONARY
	def getDict(self, grid=""):
		i = 0
		values = dict()
		for cell in self.variables:
			if grid[i]!='0':
				values[cell] = grid[i]
			else:
				values[cell] = digits
			i = i + 1
		return values