Merge pull request #304 from bluesky/302-get-constraints-function

add diffractometer get_axis_constraints() method

hkl/diffract.py

@@ -47,6 +47,7 @@ class Diffractometer(PseudoPositioner):
         ~inverse
         ~forward_solutions_table
         ~apply_constraints
+        ~get_axis_constraints
         ~reset_constraints
         ~show_constraints
         ~undo_last_constraints
@@ -540,6 +541,10 @@ def _constraints_for_databroker(self):
         ]
         # fmt: on
 
+    def get_axis_constraints(self, axis):
+        """Show the constraints for one axis."""
+        return self._constraints_dict[axis]
+
     def show_constraints(self, fmt="simple", printing=True):
         """Print the current constraints in a table."""
         tbl = pyRestTable.Table()

hkl/tests/test_diffract.py

@@ -341,3 +341,13 @@ class Q4C(hkl.E4CV):
     assert value.omega == 0.0
     assert value.chi == 0.0
     assert value.phi == 0.0
+
+
+@pytest.mark.parametrize("axis", "alpha phi omega".split())
+def test_get_constraint(axis, fourc):
+    if axis in fourc.calc._geometry.axis_names_get():
+        constraint = fourc.get_axis_constraints(axis)
+        assert isinstance(constraint, Constraint)
+    else:
+        with pytest.raises(KeyError):
+            fourc.get_axis_constraints(axis)