Raise RuntimeError when trying to apply a Wrapper to a non-Potential …

…Force (fixes #627 for now)

galpy/potential/WrapperPotential.py

@@ -10,6 +10,7 @@
     planarPotential,
 )
 from .Potential import (
+    Force,
     Potential,
     _dim,
     _evaluatephitorques,
@@ -90,6 +91,19 @@ def __init__(self, amp=1.0, pot=None, ro=None, vo=None, _init=None, **kwargs):
             return None  # Don't run __init__ at the end of setup
         Potential.__init__(self, amp=amp, ro=ro, vo=vo)
         self._pot = pot
+        # Check that we are not wrapping a non-potential Force object
+        if (
+            isinstance(self._pot, list)
+            and any(
+                [
+                    isinstance(p, Force) and not isinstance(p, Potential)
+                    for p in self._pot
+                ]
+            )
+        ) or (isinstance(self._pot, Force) and not isinstance(self._pot, Potential)):
+            raise RuntimeError(
+                "WrapperPotential cannot currently wrap non-Potential Force objects"
+            )
         self.isNonAxi = _isNonAxi(self._pot)
         # Check whether units are consistent between the wrapper and the
         # wrapped potential

tests/test_potential.py

@@ -5701,6 +5701,31 @@ def test_Wrapper_incompatibleunitserror():
     return None
 
 
+def test_Wrapper_Force_error():
+    # Test that applying a wrapper to a DissipativeForce does not currently work
+    def M(t):
+        return 1.0
+
+    # Initialize potentials and time-varying potentials
+    df = potential.ChandrasekharDynamicalFrictionForce(GMs=1.0)
+    with pytest.raises(RuntimeError) as excinfo:
+        df_wrap = potential.TimeDependentAmplitudeWrapperPotential(A=M, amp=1, pot=df)
+    assert (
+        "WrapperPotential cannot currently wrap non-Potential Force objects"
+        == excinfo.value.args[0]
+    )
+    # Also test for list
+    with pytest.raises(RuntimeError) as excinfo:
+        df_wrap = potential.TimeDependentAmplitudeWrapperPotential(
+            A=M, amp=1, pot=potential.MWPotential2014 + df
+        )
+    assert (
+        "WrapperPotential cannot currently wrap non-Potential Force objects"
+        == excinfo.value.args[0]
+    )
+    return None
+
+
 def test_WrapperPotential_unittransfer_3d():
     # Test that units are properly transferred between a potential and its
     # wrapper