Program to convert mathematical expressions into postfix notation

postfix_converter.py

operators = {'(': 0, ')': 0, '+': 1, '-': 1, '*': 2, '/': 2, '%': 2}
stack = []
postfix = []

expression = input('Enter your expression: ').split()

for ch in expression:
    if ch in operators:
        if ch is ')':
            while stack and stack[-1] is not '(':
                postfix.append(stack.pop())
            stack.pop()
            continue
        # if stack and operators[ch] <= operators[stack[-1]]:
        if stack and operators[stack[-1]] is 2 and (operators[ch] is 2 or operators[ch] is 1):
            postfix.append(stack.pop())
        stack.append(ch)
    else:
        postfix.append(ch)

for _ in range(len(stack)):
    postfix.append(stack.pop())


output = ''.join(str(e) for e in postfix)
print(output)