Cheetah/CacheStore.py

   1 """Provides several CacheStore backends for Cheetah's caching framework.  The
   2 methods provided by these classes have the same semantics as those in the
   3 python-memcached API, except for their return values:
   4
   5 set(key, val, time=0)
   6   set the value unconditionally
   7 add(key, val, time=0)
   8   set only if the server doesn't already have this key
   9 replace(key, val, time=0)
  10   set only if the server already have this key
  11 get(key, val)
  12   returns val or raises a KeyError
  13 delete(key)
  14   deletes or raises a KeyError
  15
  16 """
  17 from time import time as currentTime
  18
  19 from Cheetah.Utils.memcache import Client as MemcachedClient
  20
  21 class Error(Exception):
  22     pass
  23
  24 class AbstractCacheStore(object):
  25
  26     def set(self, key, val, time=None):
  27         raise NotImplementedError
  28
  29     def add(self, key, val, time=None):
  30         raise NotImplementedError
  31
  32     def replace(self, key, val, time=None):
  33         raise NotImplementedError
  34
  35     def delete(self, key):
  36         raise NotImplementedError
  37
  38     def get(self, key):
  39         raise NotImplementedError
  40
  41 class MemoryCacheStore(AbstractCacheStore):
  42     def __init__(self):
  43         self._data = {}
  44
  45     def set(self, key, val, time=0):
  46         self._data[key] = (val, time)
  47
  48     def add(self, key, val, time=0):
  49         if self._data.has_key(key):
  50             raise Error('a value for key %r is already in the cache'%key)
  51         self._data[key] = (val, time)
  52
  53     def replace(self, key, val, time=0):
  54         if self._data.has_key(key):
  55             raise Error('a value for key %r is already in the cache'%key)
  56         self._data[key] = (val, time)
  57
  58     def delete(self, key):
  59         del self._data[key]
  60
  61     def get(self, key):
  62         (val, exptime) = self._data[key]
  63         if exptime and currentTime() > exptime:
  64             del self._data[key]
  65             raise KeyError(key)
  66         else:
  67             return val
  68
  69     def clear(self):
  70         self._data.clear()
  71
  72 class MemcachedCacheStore(AbstractCacheStore):
  73     servers = ('127.0.0.1:11211')
  74     def __init__(self, servers=None, debug=False):
  75         if servers is None:
  76             servers = self.servers
  77
  78         self._client = MemcachedClient(servers, debug)
  79
  80     def set(self, key, val, time=0):
  81         self._client.set(key, val, time)
  82
  83     def add(self, key, val, time=0):
  84         res = self._client.add(key, val, time)
  85         if not res:
  86             raise Error('a value for key %r is already in the cache'%key)
  87         self._data[key] = (val, time)
  88
  89     def replace(self, key, val, time=0):
  90         res = self._client.replace(key, val, time)
  91         if not res:
  92             raise Error('a value for key %r is already in the cache'%key)
  93         self._data[key] = (val, time)
  94
  95     def delete(self, key):
  96         res = self._client.delete(key, time=0)
  97         if not res:
  98             raise KeyError(key)
  99
 100     def get(self, key):
 101         val = self._client.get(key)
 102         if val is None:
 103             raise KeyError(key)
 104         else:
 105             return val
 106
 107     def clear(self):
 108         self._client.flush_all()