View.py: Ignore any non-capsules and show a warning

The ugly part is the the type object is fetched using ctypes...
The types module does not expose this type.

Fixes #13

guppy/heapy/View.py

@@ -58,8 +58,10 @@ class _GLUECLAMP_:
         '_parent.Use:idset',
         '_parent.Use:iso',
         '_parent.Use:Type',
+        '_root:ctypes',
         '_root:gc',
         '_root:types',
+        '_root.warnings:warn',
     )
 
     _chgable_ = ('is_rg_update_all', 'referrers_lock', '_is_clear_drg_enabled')
@@ -139,6 +141,10 @@ def clear_drg():
     def _get_gchook_type(self):
         return Gchook_type
 
+    def _get_capsule_type(self):
+        return self.ctypes.cast(
+            self.ctypes.pythonapi.PyCapsule_Type, self.ctypes.py_object).value
+
     def _get_heapdef_modules(self):
         # We touch self.heapyc to import it & its dependent guppy.sets;
         # this is kinda specialcase-hacky but see Notes Apr 8 2005.
@@ -152,6 +158,10 @@ def _get_heapdefs(self):
                 hd = getattr(m, '_NyHeapDefs_')
             except AttributeError:
                 continue
+            if not hd or not isinstance(hd, self.capsule_type):
+                self.warn('Ignoring non-capsule object '
+                          '{}._NyHeapDefs_'.format(n))
+                continue
             heapdefs.append(hd)
         return tuple(heapdefs)