Fix amusifier Python 3.13 compatibility

src/amuse/datamodel/attributes.py

@@ -17,7 +17,7 @@ class DomainMetaclass(type):
     def __new__(metaclass, name, bases, dict):
         replacement_dictionary = {}
         for key, value in dict.items():
-            if isinstance(value, tuple):
+            if not key.startswith('__') and isinstance(value, tuple):
                 default_value, description = value
                 replacement_dictionary[key] = AttributeDefinition(
                     key, description, default_value.unit, default_value

src/amuse/datamodel/base.py

@@ -528,7 +528,7 @@ def __call__(self, *list_arguments, **keyword_arguments):
 
 def new_particle_function_attribute_with_doc(function):
     class BoundParticleFunctionAttribute(object):
-        if function.__doc__:
+        if function is not None and function.__doc__:
             __doc__ = (
                 "\n  Documentation on '{0}' particle function attribute:"
                 "\n\n".format(function.__name__) + function.__doc__