Raise error when plotting a potential with both xy=True and effective…

…=True; fixes #572

galpy/potential/Potential.py

@@ -1033,6 +1033,8 @@ def plot(
            2014-04-08 - Added effective= - Bovy (IAS)
 
         """
+        if effective and xy:
+            raise RuntimeError("xy and effective cannot be True at the same time")
         rmin = conversion.parse_length(rmin, ro=self._ro)
         rmax = conversion.parse_length(rmax, ro=self._ro)
         zmin = conversion.parse_length(zmin, ro=self._ro)
@@ -3062,6 +3064,8 @@ def plotPotentials(
        2010-07-09 - Written - Bovy (NYU)
 
     """
+    if effective and xy:
+        raise RuntimeError("xy and effective cannot be True at the same time")
     Pot = flatten(Pot)
     rmin = conversion.parse_length(rmin, **get_physical(Pot))
     rmax = conversion.parse_length(rmax, **get_physical(Pot))

tests/test_potential.py

@@ -7582,6 +7582,20 @@ def test_InterpSnapshotRZPotential_pickling():
     return None
 
 
+# Test that trying to plot a potential with xy=True and effective=True raises a RuntimeError
+def test_plotting_xy_effective_error():
+    # First a single potential
+    kp = potential.KeplerPotential(normalize=1.0)
+    with pytest.raises(RuntimeError) as excinfo:
+        kp.plot(xy=True, effective=True)
+    assert "xy and effective cannot be True at the same time" in excinfo.value.args[0]
+    # Then a list of potentials
+    with pytest.raises(RuntimeError) as excinfo:
+        potential.plotPotentials(potential.MWPotential2014, xy=True, effective=True)
+    assert "xy and effective cannot be True at the same time" in excinfo.value.args[0]
+    return None
+
+
 def test_plotting():
     import tempfile