Improve error messages when comparing against objects vs strings (#4928)

* improve error messages * whitespace fix * edit/fix error messages * add whatsnew entry * Apply suggestions from code review Co-authored-by: Ruth Comer <[email protected]> * add test Co-authored-by: Ruth Comer <[email protected]>
SciTools · Nov 1, 2022 · 8499fe0 · 8499fe0
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diff --git a/docs/src/whatsnew/latest.rst b/docs/src/whatsnew/latest.rst
@@ -79,6 +79,12 @@ This document explains the changes made to Iris for this release
 #. `@rcomer`_ removed some old redundant code that prevented determining the
  order of time cells. (:issue:`4697`, :pull:`4729`)
 
+#. `@stephenworsley`_ improved the accuracy of the error messages for
+ :meth:`~iris.cube.Cube.coord` when failing to find coordinates in the case where
+ a coordinate is given as the argument. Similarly, improved the error messages for
+ :meth:`~iris.cube.Cube.cell_measure` and :meth:`~iris.cube.Cube.ancillary_variable`.
+ (:issue:`4898`, :pull:`4928`)
+
 
 💣 Incompatible Changes
 =======================

diff --git a/lib/iris/cube.py b/lib/iris/cube.py
@@ -1990,6 +1990,12 @@ def coord(
  if name_or_coord is not None:
  if not isinstance(name_or_coord, str):
  _name = name_or_coord.name()
+ emsg = (
+ "Expected to find exactly 1 coordinate matching the given "
+ f"{_name!r} coordinate's metadata, but found none."
+ )
+ raise iris.exceptions.CoordinateNotFoundError(emsg)
+
  bad_name = _name or standard_name or long_name or ""
  emsg = (
  f"Expected to find exactly 1 {bad_name!r} coordinate, "
@@ -2194,9 +2200,15 @@ def cell_measure(self, name_or_cell_measure=None):
  bad_name = (
  name_or_cell_measure and name_or_cell_measure.name()
  ) or ""
+ if name_or_cell_measure is not None:
+ emsg = (
+ "Expected to find exactly 1 cell measure matching the given "
+ f"{bad_name!r} cell measure's metadata, but found none."
+ )
+ raise iris.exceptions.CellMeasureNotFoundError(emsg)
  msg = (
- "Expected to find exactly 1 %s cell_measure, but found "
- "none." % bad_name
+ f"Expected to find exactly 1 {bad_name!r} cell measure, "
+ "but found none."
  )
  raise iris.exceptions.CellMeasureNotFoundError(msg)
 
@@ -2281,9 +2293,16 @@ def ancillary_variable(self, name_or_ancillary_variable=None):
  name_or_ancillary_variable
  and name_or_ancillary_variable.name()
  ) or ""
+ if name_or_ancillary_variable is not None:
+ emsg = (
+ "Expected to find exactly 1 ancillary_variable matching the "
+ f"given {bad_name!r} ancillary_variable's metadata, but found "
+ "none."
+ )
+ raise iris.exceptions.AncillaryVariableNotFoundError(emsg)
  msg = (
- "Expected to find exactly 1 {!s} ancillary_variable, but "
- "found none.".format(bad_name)
+ f"Expected to find exactly 1 {bad_name!r} ancillary_variable, "
+ "but found none."
  )
  raise iris.exceptions.AncillaryVariableNotFoundError(msg)
 

diff --git a/lib/iris/tests/unit/cube/test_Cube.py b/lib/iris/tests/unit/cube/test_Cube.py
@@ -2528,6 +2528,25 @@ def test_fail_remove_ancilliary_variable_by_name(self):
  self.cube.remove_ancillary_variable("notname")
 
 
+class TestCoords(tests.IrisTest):
+ def setUp(self):
+ cube = Cube(np.arange(6).reshape(2, 3))
+ x_coord = DimCoord(points=np.array([2, 3, 4]), long_name="x")
+ cube.add_dim_coord(x_coord, 1)
+ self.x_coord = x_coord
+ self.cube = cube
+
+ def test_bad_coord(self):
+ bad_coord = self.x_coord.copy()
+ bad_coord.attributes = {"bad": "attribute"}
+ re = (
+ "Expected to find exactly 1 coordinate matching the given "
+ "'x' coordinate's metadata, but found none."
+ )
+ with self.assertRaisesRegex(CoordinateNotFoundError, re):
+ _ = self.cube.coord(bad_coord)
+
+
 class Test__getitem_CellMeasure(tests.IrisTest):
  def setUp(self):
  cube = Cube(np.arange(6).reshape(2, 3))