statement = ['1', '/', ] while (len(statement) >= 3 and len(statement) % 2): x = statement[0] y = statement[2] op = statement[1] try: x = float(x) y = float(y) # print (x, op, y, 'is equal to:') except ValueError: print('ValueError') break if (op in ['+', '-', '*', '/']): result = 0 if op == '+': result = x + y if op == '-': result = x - y if op == '*': result = x * y if op == '/': if y == 0: print('y cannot be zero!') break else: result = x / y del statement [:2] statement [0] = result if len(statement) == 1 : print(result) else: print('Wrong operator !') break else: if (len(statement) % 2 == 0) : print('Incomplete')