Python正則表達式實現(xiàn)簡易計算器功能示例

import re
class SimpleCalc(object):
  # 表達式檢測
  def check(self,exp):
    # 合法字符檢測
    res = re.findall(r"[^\d\+\-\*/\(\)\.]", exp)
    print(res)
    if res:
      print("表達式不正確?。?！")
      print("輸入了非法字符：", res)
      return False
    # 括號檢測
    res = re.findall(r"(?:[\d\)]\()|(?:\([\*/\)])|(?:[\-\+\*/]\))",exp)
    if res :
      print("表達式不正確！！！")
      print("括號使用有誤：", res)
      return False
    res = re.findall(r"\(|\)", exp)
    if res.count('(') != res.count(')'):
      print("表達式不正確?。。?)
      print("括號不匹配：", res)
      return False
    # 運算符檢測
    res = re.findall(r"[\-\+/]{2,}|\*{3,}", exp)
    if res:
      print("表達式不正確?。?！")
      print("運算符有誤：", res)
      return False
    # 小數(shù)點位置檢測
    res = re.findall(r"(^(?<=[0-9])?\.\d+)|(\.\d*?\.)|\.(\D|$)", exp)
    if res:
      print("表達式不正確?。。?)
      print("小數(shù)點位置有誤：", res)
      return False
    return True
def main():
  simpleCalc = SimpleCalc()
  while True:
    exp = input("請輸入一個正確的表達式（退出請輸入t）：\n")
    if exp == 't':
      break
    if simpleCalc.check(exp):
      print('=',eval(exp))
    else:
      continue
if __name__ == '__main__':
  main()