python custom exception handler for a class

Question

I want to build my application with a redis cache. but maybe redis is not available all the time in our case,
so I hope, it redis works well, we use it. if it can't work, just logging and ignore it this time.

for example:

try:
  conn.sadd('s', *array)
except :
  ...

since there are many place I will run some conn.{rediscommand}, I don't like to use try/except every place.

so the solution maybe :

class softcache(redis.StrictRedis):
   def sadd(key, *p):
       try:
          super(redis.StrictRedis, self).sadd(key, p)
       except:
          ..

but since redis have many commands, I have to warp them one by one.

is it possible to custom a exception handler for a class to handle all the exceptions which come from this class ?

Answer 1

Silencing per default all exceptions is probably the worst thing you can do.

Anyway, for your problem you can write a generic wrapper that just redirects to the connection object.

class ReddisWrapper(object):

    conn = conn # Here your reddis object

    def __getattr__(self, attr):

         def wrapper(*args, **kwargs):
             # Get the real reddis function
             fn = getattr(self.conn, attr)

             # Execute the function catching exceptions
             try:
                  return fn(*args, **kwargs)

             # Specify here the exceptions you expect                 
             except:
                  log(...)

         return wrapper

And then you would call like this:

reddis = ReddisWrapper()
reddis.do_something(4)

This has not been tested, and will only work with methods. For properties you should catch the non callable exception and react properly.

Answer 2

Is it always the same Exception?

If so you could write a custom, Exception catching and logging decorator.

Something like the following:

def exception_catcher(fn):
    try:
        fn()
    except Exception as e:
        log(e)

Then just use it around your code:

@exception_catcher
sadd('s', *array)

The comment and link to Exceptions for the whole class suggested by @idanshmu will offer more detailed handling of different Exceptions per method.