class NamedAndCachedAttributeType(type):
'''
In cases, where getting an attribute will
expose to the client code the detail of
the very attribute name, which could be changeable
over time.
This NamedAndCachedAttributeType is intended to
hide this detail by mapping the real attribute name
to another name that is maintained by the class itself.
By doing so, the content provider(this class) and the client
code(the caller) establish a deal that the changes of names
are taken care of by the provider itself.
Second, the value is set as a class variable once it is
first retreived, as being cached.
'''
def _raise(cls, name):
'''
Override this provide a more specific exception
'''
raise AttributeError('No name "%s" is found' % name)
def _cache(cls, name, value):
'''
The value will be cached by setting
it as the class variable
'''
setattr(cls, name, value)
def _get_value(cls, name):
'''
Override this method to do the
actual work of getting the value
'''
raise RuntimeError('_get_value() must be overidden')
def __getattr__(cls, name):
if cls.__dict__.has_key(name):
return cls.__dict__[name]
value = cls._get_value(name)
cls._cache(name, value)
return value
Diff to Previous Revision
--- revision 1 2012-08-30 10:36:37
+++ revision 2 2012-08-31 09:53:59
@@ -35,8 +35,8 @@
raise RuntimeError('_get_value() must be overidden')
def __getattr__(cls, name):
- if hasattr(cls, name):
- return getattr(cls, name)
+ if cls.__dict__.has_key(name):
+ return cls.__dict__[name]
value = cls._get_value(name)
cls._cache(name, value)
return value
