Customisation

The following classes and delegates allow customisation of different details of how Hermes works, including:

• hash algorithm

  Mangler()

  Key manager responsible for creating keys, hashing and serialisation.

  class CustomMangler(hermes.Mangler):
  
    def hash(self, value):
      return str(hash(value))
  
  cache = hermes.Hermes(
    hermes.backend.redis.Backend, mangler = CustomMangler()
  )
  

• serialisation algorithm

  Serialiser(dumps, loads)

  Serialisation delegate.

  cache = hermes.Hermes(hermes.backend.redis.Backend)
  
  # use another serialisation algorithm
  cache.mangler.serialiser = hermes.Serialiser(
    msgpack.dumps, lambda b: msgpack.loads(b, strict_map_key = False)
  )
  

• compression algorithm

  Compressor(compress, decompress, decompressError)

  Compression delegate.

  cache = hermes.Hermes(hermes.backend.redis.Backend)
  
  # disable compression
  cache.mangler.compressor = None
  
  # use another compression algorithm
  cache.mangler.compressor = hermes.Compressor(
    snappy.compress, snappy.decompress, snappy.UncompressError, 32
  )
  

• interpretation of cache operation failure (e.g. ignoring backend errors when the backend is down and calling the cached callable instead)

  Cached(frontend, callable, *[, ttl, key, tags])	Cache-point wrapper for callables and descriptors.
  CachedCoro(frontend, callable, *[, ttl, ...])	Cache-point wrapper for coroutine functions.

  class CustomCached(hermes.Cached):
  
    def __call__(self, *args, **kwargs):
      try:
        return super().__call__(*args, **kwargs)
      except redis.RedisError:
        return self._callable(*args, **kwargs)
  
  cache = hermes.Hermes(
    hermes.backend.redis.Backend, cachedcls = CustomCached
  )