def infixToPostfix(self, expr):
tokens = Token.tokenize(expr)
operatorStack = []
operandStack = []
for token in tokens:
if token.isOperand():
operandStack.append(token)
elif (token.val == OperatorType.LParen or len(operatorStack) < 1 or
OperatorType.opHierarchy(token.val) > OperatorType.opHierarchy(operatorStack[-1].val)):
operatorStack.append(token)
elif token.val == OperatorType.RParen:
# pop off both stacks building postfix expressions until LParen is found
# each postfix expression gets pushed back into the operand stack
while (operatorStack[-1].val != OperatorType.LParen):
self.__buildSinglePostfixExpr(operatorStack, operandStack)
# pop the LParen from the stack
operatorStack.pop()
elif OperatorType.opHierarchy(token.val) <= OperatorType.opHierarchy(operatorStack[-1].val):
# Continue to pop operator and operand stack, building postfix
# expressions until the stack is empty or until an operator at
# the top of the operator stack has a lower hierarchy than that
# of the token.
while (len(operatorStack) > 0 and
OperatorType.opHierarchy(token.val) <= OperatorType.opHierarchy(operatorStack[-1].val)):
print 'operators', operatorStack
print 'operands', operandStack
self.__buildSinglePostfixExpr(operatorStack, operandStack)
# push the lower prcendence operator onto stack
operatorStack.append(token)
# read in all tokens, pop stuff off the operator stack until it is empty (if it's not already)
while (len(operatorStack) > 0):
self.__buildSinglePostfixExpr(operatorStack, operandStack)
return operandStack.pop()
