Fix a bug that led to double-registration (#781)

After cloning a net, _module, _criteria, and _optimizers are already
populated. Then, when loading params, there is yet another registration,
i.e. a double registration. As a consequence, there would be two
'modules' etc. This is a fix for that.

skorch/net.py

@@ -1792,7 +1792,10 @@ def get_params(self, deep=True, **kwargs):
         # special treatment.
         params_cb = self._get_params_callbacks(deep=deep)
         params.update(params_cb)
-        return params
+
+        # don't include the following attributes
+        to_exclude = {'_modules', '_criteria', '_optimizers'}
+        return {key: val for key, val in params.items() if key not in to_exclude}
 
     def _check_kwargs(self, kwargs):
         """Check argument names passed at initialization.
@@ -2095,11 +2098,13 @@ def _register_attribute(
             self.cuda_dependent_attributes_ = (
                 self.cuda_dependent_attributes_[:] + [name + '_'])
 
-        if self.init_context_ == 'module':
+        # make sure to not double register -- this should never happen, but
+        # still better to check
+        if (self.init_context_ == 'module') and (name not in self._modules):
             self._modules = self._modules[:] + [name]
-        elif self.init_context_ == 'criterion':
+        elif (self.init_context_ == 'criterion') and (name not in self._criteria):
             self._criteria = self._criteria[:] + [name]
-        elif self.init_context_ == 'optimizer':
+        elif (self.init_context_ == 'optimizer') and (name not in self._optimizers):
             self._optimizers = self._optimizers[:] + [name]
 
     def _unregister_attribute(

skorch/tests/test_net.py

@@ -572,6 +572,44 @@ def test_save_load_state_dict_str(
         score_after = accuracy_score(y, net.predict(X))
         assert np.isclose(score_after, score_before)
 
+    def test_save_load_state_dict_no_duplicate_registration_after_initialize(
+            self, net_cls, module_cls, net_fit, tmpdir):
+        # #781
+        net = net_cls(module_cls).initialize()
+
+        p = tmpdir.mkdir('skorch').join('testmodel.pkl')
+        with open(str(p), 'wb') as f:
+            net_fit.save_params(f_params=f)
+        del net_fit
+
+        with open(str(p), 'rb') as f:
+            net.load_params(f_params=f)
+
+        # check that there are no duplicates in _modules, _criteria, _optimizers
+        # pylint: disable=protected-access
+        assert net._modules == ['module']
+        assert net._criteria == ['criterion']
+        assert net._optimizers == ['optimizer']
+
+    def test_save_load_state_dict_no_duplicate_registration_after_clone(
+            self, net_fit, tmpdir):
+        # #781
+        net = clone(net_fit).initialize()
+
+        p = tmpdir.mkdir('skorch').join('testmodel.pkl')
+        with open(str(p), 'wb') as f:
+            net_fit.save_params(f_params=f)
+        del net_fit
+
+        with open(str(p), 'rb') as f:
+            net.load_params(f_params=f)
+
+        # check that there are no duplicates in _modules, _criteria, _optimizers
+        # pylint: disable=protected-access
+        assert net._modules == ['module']
+        assert net._criteria == ['criterion']
+        assert net._optimizers == ['optimizer']
+
     @pytest.fixture(scope='module')
     def net_fit_adam(self, net_cls, module_cls, data):
         net = net_cls(
@@ -1426,6 +1464,15 @@ def test_get_params_works(self, net_cls, module_cls):
         # now initialized
         assert 'callbacks__myscore__scoring' in params
 
+    def test_get_params_no_unwanted_params(self, net, net_fit):
+        # #781
+        # make sure certain keys are not returned
+        keys_unwanted = {'_modules', '_criteria', '_optimizers'}
+        for net_ in (net, net_fit):
+            keys_found = set(net_.get_params())
+            overlap = keys_found & keys_unwanted
+            assert not overlap
+
     def test_get_params_with_uninit_callbacks(self, net_cls, module_cls):
         from skorch.callbacks import EpochTimer