>>> class A(object):
...     """
...     """
...
>>> PyType_Check(A())
False
>>> PyType_Check(dict())
True

>>> issubclass(dict, type)
False
>>> isinstance(dict(), type)
False
>>> isinstance(A(), type)
False
>>> issubclass(dict, type)
False
>>> issubclass(A, type)
False

   /* Sanity check the value given to make sure it is allowed in the cache */
    if (PyType_Check(v)) {
        /* Its a persistent class, such as a ZClass. Thats ok. */
    }
    else if (v->ob_type->tp_basicsize < sizeof(cPersistentObject)) {
        /* If it's not an instance of a persistent class, (ie Python
	   classes that derive from persistent.Persistent, BTrees,
	   etc), report an error.
	   TODO:  checking sizeof() seems a poor test.
	*/
	PyErr_SetString(PyExc_TypeError,
			"Cache values must be persistent objects.");
	return -1;
    }

>>> class A(object):
...             ""
>>> isinstance(dict, type)
True
>>> isinstance(A, type)
True

>>> a = A()
>>> (type(a) == types.TypeType) or issubclass(a.__class__,  types.TypeType)

(type(a) == types.TypeType) or issubclass(a.__class__,  types.TypeType)

(type(a) == type) or issubclass(a.__class__,  type)