infix to postfix python code
class stack:
def __init__(self):
self.item = []
def push(self,it):
self.item.append(it)
def peek(self):
if self.isempty() == True:
return 0
return self.item[-1]
def pop(self):
if self.isempty() == True:
return 0
return(self.item.pop())
def length(self):
return (len(self.item))
def isempty(self):
if self.item == []:
return True
else:
return False
def display(self):
if self.isempty()== True:
return
temps = stack()
while(self.isempty() != True):
x = self.peek()
print("~",x)
temps.push(x)
self.pop()
while(temps.isempty() != True):
x = temps.peek()
self.push(x)
temps.pop()
def isOperand(self, ch):
return ch.isalpha()
def notGreater(self, i):
precedence = {'+':1, '-':1, '*':2, '/':2, '%':2, '^':3}
if self.peek() == '(':
return False
a = precedence[i]
b = precedence[self.peek()]
if a <= b:
return True
else:
return False
def infixToPostfix(self, exp):
output = ""
for i in exp:
if self.isOperand(i) == True: # check if operand add to output
print(i,"~ Operand push to stack")
output = output + i
# If the character is an '(', push it to stack
elif i == '(':
self.push(i)
print(i," ~ Found ( push into stack")
elif i == ')': # if ')' pop till '('
while( self.isempty() != True and self.peek() != '('):
n = self.pop()
output = output + n
print(n, "~ Operator popped from stack")
if (self.isempty() != True and self.peek() != '('):
print("_________")
return -1
else:
x = self.pop()
print(x, "Popping and deleting (")
else:
while(self.isempty() != True and self.notGreater(i)):
c = self.pop()
output = output + c
print(c,"Operator popped after checking precedence from stack")
self.push(i)
print(i,"Operator pushed to stack")
# pop all the operator from the stack
while self.isempty() != True:
xx = self.pop()
output = output + xx
print(xx,"~ pop at last")
print(output)
self.display()
st = stack()
st.infixToPostfix("a+(b*c)")