Unit Converter (python)

gistfile1.py

class UnitConverter (object):
	def __init__ (self):
		self.conv = {}

	def connect (self, a, b, k):
		self.conv[a][b] = k
		self.conv[b][a] = 1.0 / k

		for c in self.conv[a].keys():
			if c != b and c not in self.conv[b].keys():
				self.connect(c, b, self.conv[c][a] * self.conv[a][b])

		for d in self.conv[b].keys():
			if d != a and d not in self.conv[a].keys():
				self.connect(d, a, self.conv[d][b] * self.conv[b][a])

	def addConversion (self, a, b, k):
		if a not in self.conv:
			self.conv[a] = {}
		if b not in self.conv:
			self.conv[b] = {}
		self.connect(a, b, k)

	def convert (self, from_, to):
		return self.conv[from_][to]

	def printConversion (self, from_, to, value):
		try:
			return "%s %s = %s %s"%(value, from_, self.conv[from_][to] * value, to)
		except KeyError:
			return "Cannot convert %s to %s"%(from_, to)
			
if __name__  == '__main__':
	uc = UnitConverter()
	uc.addConversion('m', 'cm', 100.0)
	uc.addConversion('cm', 'mm', 10.0)
	uc.addConversion('km', 'm', 1000.0)

	uc.addConversion('ft', 'in', 12.0)
	uc.addConversion('mi', 'ft', 5280.0)
	uc.addConversion('in', 'cm', 2.54)

	print("Conversions:")
	print('\n'.join(['\t%s: %s'%(k, v) for k, v in uc.conv.iteritems()]))

	print(uc.printConversion('cm', 'm', 50))
	print(uc.printConversion('m', 'mm', 45))
	print(uc.printConversion('mm', 'm', 35))
	print(uc.printConversion('m', 'ft', 1))
	print(uc.printConversion('km', 'mi', 10))