def infix_to_postfix(infixexpr):
"""Converts an infix expression to an equivalent postfix expression """
prec = {'^':4, '*': 3, '/': 3, '+': 2, '-': 2, '(': 1}
opstack = StackArray(30)
postfixList = []
tokenList = infixexpr.split(' ')#returns an array with elements split
for tok in tokenList:
if tok not in "^*()-/+": #if token is a number put in the list
postfixList.append(tok)
elif tok == '(': #if token is open parenthesis put it in list output
opstack.push(tok)
elif tok == ')': #if token is close parenthesis
toptoken = opstack.pop() #take the top token of stack
while toptoken != '(': #pop through the stack and append to output list until you get to the open parenthesis
postfixList.append(toptoken)
toptoken = opstack.pop()
else:
while (not opstack.is_empty()) and (prec[opstack.peek()] >= prec[tok]):#handle precedence
if opstack.peek() == '^' and tok == "^":
break#dont append
postfixList.append(opstack.pop())
opstack.push(tok)
while not opstack.is_empty():#if empty append everything else
postfixList.append(opstack.pop())
return " ".join(postfixList)
def infix_to_postfix(infixexpr):
"""Converts an infix expression to an equivalent postfix expression """
"""Signature: a string containing an infix expression where tokens are space separated is
the single input parameter and returns a string containing a postfix expression
where tokens are space separated"""
operandStack = StackArray(30)
postfixList = []
tokenList = infixexpr.split()
precedence = {"^": 4, "*": 3, "/": 3, "+": 2, "-": 2, "(": 1}
for token in tokenList:
if is_valid(token):
postfixList.append(token)
else:
if token == '(':
operandStack.push(token)
elif token == ')':
top = operandStack.pop()
while top != '(':
postfixList.append(top)
top = operandStack.pop()
else:
while (operandStack.is_empty() == False) and (
precedence[operandStack.peek()] >= precedence[token]
and token != "^"):
postfixList.append(operandStack.pop())
operandStack.push(token)
while operandStack.is_empty() == False:
postfixList.append(operandStack.pop())
return " ".join(postfixList)
def infix_to_postfix(infix_expr):
# converts infix expression to a postfix expression
""" Method to convert infix expressions into postix
Infix expression should have operations and operands seperated by spaces
postfix expression will be formatted that way"""
expression = infix_expr.split(" ")
# operands = StackArray(len(expression)//2)
operands = StackArray(30)
to_process = []
for part in expression:
# part = expression[i]
if not check_num(part):
if (part == ')'):
while (operands.peek() != '('):
to_process.append(str(operands.pop()))
operands.pop()
# print("Operand: " + part);
else:
while (not operandOnTop(part, operands)):
to_process.append(str(operands.pop()))
operands.push(part);
# print("Operand: " + part);
else:
if check_float(part):
to_process.append(float(part))
else:
to_process.append(int(part))
while (not operands.is_empty()):
to_process.append(str(operands.pop()))
postfix_expr = " ".join(str(thing) for thing in to_process)
# print("Postfix Expression Ready: " + postfix_expr)
return postfix_expr
def infix_to_postfix(infixexpr):
"""Converts an infix expression to an equivalent postfix expression """
"""Signature: a string containing an infix expression where tokens are space separated is
the single input parameter and returns a string containing a postfix expression
where tokens are space separated"""
newStack = StackArray(30)
postfixList= []
tokenList = infixexpr.split()
x = 0
par = 0
while x < len(tokenList):
if tokenList[x] is ('('): #When encountering paranthesis in the input
newStack.push(tokenList[x])
par = x+1
while par < len(tokenList) and tokenList[par] not in (')'):
if tokenList[par] not in ('*','-','/','+','^','('):
postfixList.append(tokenList[par])
elif tokenList[par] in ('('):
newStack.push(tokenList[x])
elif tokenList[par] in ('^'):
if newStack.peek() in ('('):
newStack.push(tokenList[par])
elif newStack.peek() in '^':
newStack.push(tokenList[par])
elif newStack.peek() in ('*','/'):
newStack.push(tokenList[par])
elif newStack.peek() in ('+','-'):
newStack.push(tokenList[par])
elif tokenList[par] in ('*','/'):
if newStack.peek() in ('('):
newStack.push(tokenList[par])
elif newStack.peek() in ('^'):
postfixList.append(newStack.pop())
newStack.push(tokenList[par])
elif newStack.peek() in ('+','-'):
newStack.push(tokenList[par])
elif newStack.peek() in ('*','/'):
postfixList.append(newStack.pop())
newStack.push(tokenList[par])
elif tokenList[par] in ('+','-'):
if newStack.peek() in ('('):
newStack.push(tokenList[par])
elif newStack.peek() in ('^','*','/'):
while newStack.peek() in ('^','*','/') and newStack.peek() not in ('(') :
postfixList.append(newStack.pop())
newStack.push(tokenList[par])
elif newStack.peek() in ('+','-'):
while newStack.peek() in ('+','-'):
postfixList.append(newStack.pop())
newStack.push(tokenList[par])
par+=1
condition = True
while condition: #Popping and appending remaining symbols to list
while newStack.peek() not in ('('):
postfixList.append(newStack.pop())
newStack.pop() #Removing the ( that was pushed onto the Stack
iterate = 0
if newStack.size() == 0:
condition = False
while iterate < newStack.size():
if newStack.items[iterate] == None:
iterate+=1
continue
elif newStack.items[iterate] in ('('):
condition = True
break
else:
iterate+=1
condition = False
x = par
elif tokenList[x] not in ('*','-','/','+','^','(',')'): #Encountering a non paranthesis
postfixList.append(tokenList[x])
elif tokenList[x] in ('^'):
if newStack.is_empty():
newStack.push(tokenList[x])
elif newStack.peek() in '^':
newStack.push(tokenList[x])
elif newStack.peek() in ('*','/'):
newStack.push(tokenList[x])
elif newStack.peek() in ('+','-'):
newStack.push(tokenList[x])
elif tokenList[x] in ('*','/'):
if newStack.is_empty():
newStack.push(tokenList[x])
elif newStack.peek() in ('^'):
postfixList.append(newStack.pop())
newStack.push(tokenList[x])
elif newStack.peek() in ('+','-'):
newStack.push(tokenList[x])
elif newStack.peek() in ('*','/'):
postfixList.append(newStack.pop())
newStack.push(tokenList[x])
elif tokenList[x] in ('+','-'):
if newStack.is_empty():
newStack.push(tokenList[x])
elif newStack.peek() in ('^','*','/'):
while newStack.peek() in ('^','*','/') or not newStack.is_empty():
postfixList.append(newStack.pop())
newStack.push(tokenList[x])
elif newStack.peek() in ('+','-'):
while newStack.peek() in ('+','-'):
postfixList.append(newStack.pop())
newStack.push(tokenList[x])
x+=1
while not newStack.is_empty(): #Popping and appending remaining symbols to list
postfixList.append(newStack.pop())
return " ".join(postfixList) #Creates the Postfix Expression by joining the list