gray2.py - Iterative Gray code g

#!/usr/bin/python# Gray code by iterative approach. Public domain. pearfalse.co.ukclass GrayCode:	"""	Creates a GrayCode proxy object. This object is iterable.		__init__(self, n)		n = number of bits of gray code required		example:		from gray2 import GrayCode		for gc in iter(GrayCode(4)):			print "%d%d%d%d | %d" % (				(1 if gc & 0x8 else 0),				(1 if gc & 0x8 else 0),				(1 if gc & 0x8 else 0),				(1 if gc & 0x8 else 0),				gc			)		"""	def __init__(self, n):		#n = ; number of bits required		#t = 0 ; total gray code value so far		#i = 0 ; iteration variable		self.n = n			def __iter__(self):		self.t = self.i = 0		return self			def next(self):		if self.i == 2**self.n: raise StopIteration		t = 0		# t |= (ith bit xor (i+1)th bit)		for pos in range(self.n-1, -1, -1):			#print "n=%d, t=%x, i=%d, pos=%d" % (self.n, t, self.i, pos)			bitat = (self.i >> (pos)) & 0x1			bitb4 = (self.i >> (pos+1)) & 0x1			#print "%d => %d %d" % (self.i, bitb4, bitat)			t <<= 1			t |= (bitat ^ bitb4)				self.i += 1		return t		if __name__ == '__main__':	for gc in iter(GrayCode(4)):		print "%d%d%d%d | %d" % (			(1 if gc & 0x8 else 0),			(1 if gc & 0x4 else 0),			(1 if gc & 0x2 else 0),			(1 if gc & 0x1 else 0),			gc		)