def eval_infix(infix_exp):
operands = Stack()
op_stack = Stack()
infix = infix_exp.split()
for sym in infix:
if sym.isdigit():
operands.push(sym)
elif sym == "(":
op_stack.push(sym)
elif sym == ")":
second = float(operands.pop())
first = float(operands.pop())
op = op_stack.pop()
operands.push(operators[op](first, second))
op_stack.pop()
elif sym in operators.keys():
if not op_stack.isEmpty() and precedence[op_stack.peek()] >= precedence[sym]:
op = op_stack.pop()
second = float(operands.pop())
first = float(operands.pop())
operands.push(operators[op](first, second))
op_stack.push(sym)
while not operands.size() == 1:
second = float(operands.pop())
first = float(operands.pop())
op = op_stack.pop()
operands.push(operators[op](first, second))
return operands.pop()
def infix_to_postfix(infix_exp):
operators = Stack()
infix_exp = infix_exp.split()
postfix = []
for sym in infix_exp:
if sym in string.ascii_letters or sym.isdigit():
postfix.append(sym)
elif sym == "(":
operators.push(sym)
elif sym == ")":
while not operators.peek() == "(":
postfix.append(operators.pop())
operators.pop()
elif sym in precedence.keys():
while not operators.isEmpty() and precedence[operators.peek()] >= precedence[sym]:
postfix.append(operators.pop())
operators.push(sym)
else:
raise TypeError("Wrong expression")
while not operators.isEmpty():
postfix.append(operators.pop())
return " ".join(postfix)
def general_parentheses_checker(expression):
sym_dict = {')':'(', '}': '{', ']': '['}
s = Stack()
for symbol in expression:
if symbol in '([{':
s.push(symbol)
elif symbol in ')]}':
if s.isEmpty():
return False
else:
if sym_dict[symbol] == s.peek():
s.pop()
else:
return False
if s.isEmpty():
return True
else:
return False
