def iftopf(expression, order):
#Infix to postfix conversion
s = Stack()
pf = []
query_terms = expression.split(' ')
for term in query_terms:
if term not in (["OR", "AND", "NOT", "(", ")"]):
term = stemmer.stem(term, 0, len(term) - 1)
id1 = get_id(term)
pf.append(id1)
elif term == '(':
s.push(term)
elif term == ')':
topterm = s.pop()
while topterm != '(':
pf.append(topterm)
topterm = s.pop()
else:
if (not s.isEmpty() and s.peek() == "NOT"):
pf.append(s.pop())
while (not s.isEmpty()) and (order[s.peek()] >= order[term]
and term != "NOT"):
pf.append(s.pop())
s.push(term)
while not s.isEmpty():
pf.append(s.pop())
return pf
def infix_to_postfix(token_list):
stack = Stack()
postfix_list = []
for token in token_list:
if token.isalpha() or token.isdecimal():
postfix_list.append(token)
elif token == '(':
stack.push(token)
elif token == ')':
top_token = stack.pop()
while top_token != '(':
postfix_list.append(top_token)
top_token = stack.pop()
else:
while not stack.isEmpty() and OPERATORS_PRECEDENCE[
stack.peek()] >= OPERATORS_PRECEDENCE[token]:
postfix_list.append(stack.pop())
stack.push(token)
while not stack.isEmpty():
postfix_list.append(stack.pop())
return postfix_list
def infixToPostfix(infixexpr):
prec = {
'*': 3,
'/': 3,
'+': 2,
'-': 2,
'(': 1,
}
opStack = Stack()
postfixList = []
tokenList = infixexpr.split()
for token in tokenList:
if token in "ABCDEFGHIJKLMNOPQRSTUVWXYZ" or token in "0123456789":
postfixList.append(token)
elif token == '(':
opStack.push(token)
elif token == ')':
topToken = opStack.pop()
while topToken != '(':
postfixList.append(topToken)
topToken = opStack.pop()
else:
while (not opStack.isEmpty()) and \
(prec[opStack.peek()] >= prec[token]):
postfixList.append(opStack.pop())
opStack.push(token)
while not opStack.isEmpty():
postfixList.append(opStack.pop())
return ''.join(postfixList)
def toPostfix(infixString):
s = Stack()
output = []
infixString = infixString.split()
for i in infixString:
if i.isalnum():
output.append(i)
elif i == '(':
s.push(i)
elif i == ')':
top = s.pop()
while top != '(':
output.append(top)
top = s.pop()
else:
while (not s.isEmpty()) and (prec[s.peek()] > prec[i]):
output.append(s.pop())
s.push(i)
while not s.isEmpty():
output.append(s.pop())
return " ".join(output)
