########## First define the interface checker and interfaces
from sets import Set
import UserDict
class InterfaceOmission(Exception): pass
class InterfaceChecker(type):
"Validates the presence of required attributes"
def __new__(cls, classname, bases, classdict):
obj = type(classname, bases, classdict)
if '__implements__' in classdict:
defined = Set(dir(obj))
for interface in classdict['__implements__']:
required = Set(dir(interface))
if not required.issubset(defined):
raise InterfaceOmission, list(required - defined)
return obj
class MinimalMapping(object):
"Interface specification"
def __getitem__(self, key): pass
def __setitem__(self, key, value): pass
def __delitem__(self, key): pass
def __contains__(self, key): pass
class FullMapping(MinimalMapping, UserDict.DictMixin):
pass
class MinimalSequence(object):
def __len__(self): pass
def __getitem__(self, index): pass
class Callable(object):
def __call__(self, *args): pass
########## The user code starts here
class MyClass(object):
__metaclass__ = InterfaceChecker
__implements__ = [MinimalMapping, Callable]
def __getitem__(self, key): pass
def __setitem__(self, key, value): pass
#def __delitem__(self, key): pass
def __contains__(self, key): pass
def __call__(self, *args): pass
def setdefault(self, key, default):
'Not required by the interface'
m = MyClass()
assert MinimalMapping in m.__implements__
