Polish notation using two stacks

polish_notation.py

def solve(polish_notation):
  polish_notation = polish_notation.split()
  operands = []
  operators = []
  operations = {
    '+': lambda x, y: x + y,
    '-': lambda x, y: x - y,
    '*': lambda x, y: x * y,
    '/': lambda x, y: x / y
  }

  last_read = None
  for element in polish_notation:
    if element.isdigit():
      operands.append(int(element))

      while len(operands) > 1 and last_read.isdigit():
        second = operands.pop()
        first = operands.pop()
        operator = operators.pop()
        operands.append(operations[operator](first, second))
    else:
      operators.append(element)

    last_read = element
    
  return operands.pop()


if __name__ == '__main__':
  print(solve('* + 3 5 - 7 2'))
  print(solve('- * / 15 - 7 + 1 1 3 + 2 + 1 1'))