From 1ea6a4d3baba4ff2adb187c342b6bd9b2b9c78d7 Mon Sep 17 00:00:00 2001
From: "Matthew W. Thompson" <matt.thompson@vanderbilt.edu>
Date: Tue, 30 Jun 2020 16:35:55 -0500
Subject: [PATCH 1/2] ENH: Add ForceField.registered_parameter_handlers
 property

---
 openforcefield/tests/test_forcefield.py       | 20 +++++++++++++++++++
 .../typing/engines/smirnoff/forcefield.py     | 13 ++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/openforcefield/tests/test_forcefield.py b/openforcefield/tests/test_forcefield.py
index c3419c1e4..12e62371e 100644
--- a/openforcefield/tests/test_forcefield.py
+++ b/openforcefield/tests/test_forcefield.py
@@ -1211,6 +1211,26 @@ def test_nonbonded_method_resolution(self,
                 forcefield.get_parameter_handler('Electrostatics', {}).method = electrostatics_method
                 omm_system = forcefield.create_openmm_system(topology)
 
+    def test_registered_parameter_handlers(self):
+        """Test registered_parameter_handlers property"""
+        forcefield = ForceField('test_forcefields/smirnoff99Frosst.offxml')
+        registered_handlers = forcefield.registered_parameter_handlers
+
+        expected_handlers = [
+            'Bonds',
+            'Angles',
+            'ProperTorsions',
+            'ImproperTorsions',
+            'vdW',
+            'Electrostatics',
+            'ToolkitAM1BCC',
+        ]
+
+        for expected_handler in expected_handlers:
+            assert expected_handler in registered_handlers
+
+        assert 'LibraryChrages' not in registered_handlers
+
     def test_parameter_handler_lookup(self):
         """Ensure __getitem__ lookups work"""
         forcefield = ForceField('test_forcefields/smirnoff99Frosst.offxml')
diff --git a/openforcefield/typing/engines/smirnoff/forcefield.py b/openforcefield/typing/engines/smirnoff/forcefield.py
index 6ab10266a..dd4a3f13f 100644
--- a/openforcefield/typing/engines/smirnoff/forcefield.py
+++ b/openforcefield/typing/engines/smirnoff/forcefield.py
@@ -556,6 +556,19 @@ def register_parameter_io_handler(self, parameter_io_handler):
                     self._parameter_io_handlers[io_format]))
         self._parameter_io_handlers[io_format] = parameter_io_handler
 
+    @property
+    def registered_parameter_handlers(self):
+        """
+        Return the list of registered parameter handlers by name
+
+        .. warning :: This API is experimental and subject to change.
+
+        Returns
+        -------
+            registered_parameter_handlers: iterable of names of ParameterHandler objects in this ForceField
+
+        """
+        return [*self._parameter_handlers.keys()]
 
     # TODO: Do we want to make this optional?
 

From 72c2c82f3c058bcc8ca927cd81adc8f14e394195 Mon Sep 17 00:00:00 2001
From: "Matthew W. Thompson" <matt.thompson@vanderbilt.edu>
Date: Mon, 6 Jul 2020 09:39:00 -0500
Subject: [PATCH 2/2] DOCS: Update changelog for PR #632

---
 docs/releasehistory.rst | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/docs/releasehistory.rst b/docs/releasehistory.rst
index ed5df35eb..c2201e693 100644
--- a/docs/releasehistory.rst
+++ b/docs/releasehistory.rst
@@ -17,6 +17,12 @@ Bugfixes
   would not load files correctly if passed lowercase `file_format`. Note that this bug did not occur when calling
   :`Molecule.from_file` <openforcefield.topology.molecule.Molecule.from_file>`.
 
+New features
+""""""""""""
+- `PR #632 <https://github.com/openforcefield/openforcefield/pull/632>`_: Adds
+  :py:meth:`ForceField.registered_parameter_handlers 
+  <openforcefield.typing.engines.smirnoff.forcefield.ForceField.registered_parameter_handlers>`
+
 0.7.0 - Charge Increment Model, Proper Torsion interpolation, and new Molecule methods
 --------------------------------------------------------------------------------------