python 装饰器的坑

今天研究了下装饰器，添加重试功能遇到了个坑，跟大家分享一下；

代码如下：

 def re_try(maxtry):
     print locals()
     def wrapper(fn):
         print locals()
         def _wrapper(*args, **kwargs):
             print locals()
             while maxtry > 0:
                 try:
                     return fn(*args, **kwargs)
                 except Exception as e:
                     print e.message
                 maxtry -= 1
         return _wrapper
     return wrapper

 @re_try(4)
 def test(a, b):
     # return a+b
     if DEC == 2:
         return a+b
     else:
         raise WrapException

 def main():
     print test(3,5)

 if __name__ == '__main__':
     main()

运行的结果如下：

{'maxtry': 4}
{'fn': <function test at 0x024B5170>}
{'args': (3, 5), 'fn': <function test at 0x024B5170>, 'kwargs': {}}
Traceback (most recent call last):
  File "D:\myGit\test\testWrapp.py", line 58, in <module>
    main()
  File "D:\myGit\test\testWrapp.py", line 55, in main
    print test(3,5)
  File "D:\myGit\test\testWrapp.py", line 17, in _wrapper
    while maxtry > 0:
UnboundLocalError: local variable 'maxtry' referenced before assignment

按道理maxtry这个变量会一直存在再整个装饰器运行过程中，但是我们看到在第4行 和第6 行并没有看到该变量，本农百思不得七姐,于是就瞎调试，终于实现了功能。

 def re_try(max_try):
     print locals()
     def wrapper(func):
         print locals()
         @wraps(func)
         def _wrapper(*args, **kw):
             print locals()
             for i in xrange(max_try):
                 try:
                     res = func(*args, **kw)
                     if res is None:
                         continue
                     else:
                         return res
                 except Exception as e:
                     print e.message
         return _wrapper
     return wrapper

 @re_try(4)
 def test(a, b):
     # return a+b
     if DEC == 2:
         return a+b
     else:
         raise WrapException

 def main():
     print test(3,5)

 if __name__ == '__main__':
     main()

把while 循环改成了for循环，得到如下运行结果：

{'max_try': 4}
{'max_try': 4, 'func': <function test at 0x02613170>}
{'args': (3, 5), 'kw': {}, 'func': <function test at 0x02613170>, 'max_try': 4}

虽然目前还不知道为什么装饰器内部函数里面不能使用while，但是目前先记下来，日后觅得真理再来更新。