def convert(self):
# cache the result
if not self._pfTokens:
# save the converted expression (tokens)
self._pfTokens = []
# stack to store operators and operands
stack = LinkedStack()
for token in self._scanner:
# append the operand to list
if not token.isOperator():
self._pfTokens.append(token)
# Token.OPENPAREN & Token.CLOSEPAREN are operators,
# so must be called before token.isOperator().
elif token.getType() == Token.OPENPAREN:
stack.push(token)
elif token.getType() == Token.CLOSEPAREN:
for i in range(len(stack)):
operator = stack.pop()
if operator.getType() == Token.OPENPAREN:
break
self._pfTokens.append(operator)
elif token.isOperator():
# pop operators in the stack whose precedence is not smaller
for i in range(len(stack)):
if (stack.peek().getType() == Token.OPENPAREN
or stack.peek().getPrecedence() <
token.getPrecedence()):
break
self._pfTokens.append(stack.pop())
stack.push(token)
for i in range(len(stack)):
self._pfTokens.append(stack.pop())
return self._pfTokens
def is_palindrome(word):
stack = LinkedStack()
for index in range(len(word) // 2):
stack.push(word[index])
for index in range((len(word) + 1) // 2, len(word)):
if stack.peek() == word[index]:
stack.pop()
else:
return False
return True
class Translator(object):
"""Translates infix expressions to postfix expressions."""
def __init__(self, scanner):
"""Sets the initial state of the translator."""
self._expressionSoFar = ""
self._operatorStack = LinkedStack()
self._scanner = scanner
def translate(self):
"""Returns a list of tokens that represent the postfix
form of sourceStr. Assumes that the infix expression
in sourceStr is syntactically correct"""
postfix = list()
for currentToken in self._scanner:
self._expressionSoFar += str(currentToken) + " "
if currentToken.getType() == Token.INT:
postfix.append(currentToken)
elif currentToken.getType() == Token.LPAR:
self._operatorStack.push(currentToken)
elif currentToken.getType() == Token.RPAR:
topOperator = self._operatorStack.pop()
while topOperator.getType() != Token.LPAR:
postfix.append(topOperator)
topOperator = self._operatorStack.pop()
else:
while not self._operatorStack.isEmpty() and \
self._operatorStack.peek().getPrecedence() >= \
currentToken.getPrecedence():
postfix.append(self._operatorStack.pop())
self._operatorStack.push(currentToken)
while not self._operatorStack.isEmpty():
postfix.append(self._operatorStack.pop())
return postfix
def __str__(self):
"""Returns a string containing the contents of the expression
processed and the stack to this point."""
result = "\n"
if self._expressionSoFar == "":
result += "Portion of expression processed: none\n"
else:
result += "Portion of expression processed: " + \
self._expressionSoFar + "\n"
if self._operatorStack.isEmpty():
result += "The stack is empty"
else:
result += "Operators on the stack : " + \
str(self._operatorStack)
return result
def translationStatus(self):
return str(self)
class Translator(object):
"""Translates infix expressions to postfix expressions."""
def __init__(self, scanner):
"""Sets the initial state of the translator."""
self._expressionSoFar = ""
self._operatorStack = LinkedStack()
self._scanner = scanner
def translate(self):
"""Returns a list of tokens that represent the postfix
form of sourceStr. Assumes that the infix expression
in sourceStr is syntactically correct"""
postfix = list()
for currentToken in self._scanner:
self._expressionSoFar += str(currentToken) + " "
if currentToken.getType() == Token.INT:
postfix.append(currentToken)
elif currentToken.getType() == Token.LPAR:
self._operatorStack.push(currentToken)
elif currentToken.getType() == Token.RPAR:
topOperator = self._operatorStack.pop()
while topOperator.getType() != Token.LPAR:
postfix.append(topOperator)
topOperator = self._operatorStack.pop()
else:
while not self._operatorStack.isEmpty() and \
self._operatorStack.peek().getPrecedence() >= \
currentToken.getPrecedence():
postfix.append(self._operatorStack.pop())
self._operatorStack.push(currentToken)
while not self._operatorStack.isEmpty():
postfix.append(self._operatorStack.pop())
return postfix
def __str__(self):
"""Returns a string containing the contents of the expression
processed and the stack to this point."""
result = "\n"
if self._expressionSoFar == "":
result += "Portion of expression processed: none\n"
else:
result += "Portion of expression processed: " + \
self._expressionSoFar + "\n"
if self._operatorStack.isEmpty():
result += "The stack is empty"
else:
result += "Operators on the stack : " + \
str(self._operatorStack)
return result
def translationStatus(self):
return str(self)
def is_palindrome(self, word):
# check if word is palindrome
half_1, half_2 = word[:len(word) // 2], word[len(word) // 2:]
# cut first letter, whcih is not important
if len(half_2) != len(half_1):
half_2 = half_2[1:]
stack = LinkedStack()
for let in half_1:
stack.push(let)
for i in range(len(half_2)):
if half_2[i] != stack.peek():
return 0
stack.pop()
return 1
def lipeek_unit_test(self):
temp = LinkedStack()
for count in range(5):
temp.push(count+1)
self.assertEqual(temp.peek(), 5)
