Make default STEP_METHODS a list that can be modified

pymc/step_methods/__init__.py

@@ -12,7 +12,7 @@
 #   See the License for the specific language governing permissions and
 #   limitations under the License.
 
-from pymc.step_methods.compound import CompoundStep
+from pymc.step_methods.compound import BlockedStep, CompoundStep
 from pymc.step_methods.hmc import NUTS, HamiltonianMC
 from pymc.step_methods.metropolis import (
     BinaryGibbsMetropolis,
@@ -30,12 +30,13 @@
 )
 from pymc.step_methods.slicer import Slice
 
-STEP_METHODS = (
+# Other step methods can be added by appending to this list
+STEP_METHODS: list[type[BlockedStep]] = [
     NUTS,
     HamiltonianMC,
     Metropolis,
     BinaryMetropolis,
     BinaryGibbsMetropolis,
     Slice,
     CategoricalGibbsMetropolis,
-)
+]

tests/sampling/test_mcmc.py

@@ -762,12 +762,18 @@ def kill_grad(x):
                 steps = assign_step_methods(model, [])
         assert isinstance(steps, Slice)
 
-    def test_modify_step_methods(self):
+    @pytest.fixture
+    def step_methods(self):
+        """Make sure we reset the STEP_METHODS after the test is done."""
+        methods_copy = pm.STEP_METHODS.copy()
+        yield pm.STEP_METHODS
+        pm.STEP_METHODS.clear()
+        for method in methods_copy:
+            pm.STEP_METHODS.append(method)
+
+    def test_modify_step_methods(self, step_methods):
         """Test step methods can be changed"""
-        # remove nuts from step_methods
-        step_methods = list(pm.STEP_METHODS)
         step_methods.remove(NUTS)
-        pm.STEP_METHODS = step_methods
 
         with pm.Model() as model:
             pm.Normal("x", 0, 1)
@@ -776,7 +782,7 @@ def test_modify_step_methods(self):
         assert not isinstance(steps, NUTS)
 
         # add back nuts
-        pm.STEP_METHODS = [*step_methods, NUTS]
+        step_methods.append(NUTS)
 
         with pm.Model() as model:
             pm.Normal("x", 0, 1)

tests/step_methods/test_compound.py

@@ -26,7 +26,6 @@
     Slice,
 )
 from pymc.step_methods.compound import (
-    BlockedStep,
     StatsBijection,
     flatten_steps,
     get_stats_dtypes_shapes_from_steps,
@@ -38,10 +37,7 @@
 
 
 def test_all_stepmethods_emit_tune_stat():
-    attrs = [getattr(pm.step_methods, n) for n in dir(pm.step_methods)]
-    step_types = [
-        attr for attr in attrs if isinstance(attr, type) and issubclass(attr, BlockedStep)
-    ]
+    step_types = pm.step_methods.STEP_METHODS
     assert len(step_types) > 5
     for cls in step_types:
         assert "tune" in cls.stats_dtypes_shapes