Allowing exemption to axis guessing on coords

lib/iris/coords.py

@@ -861,7 +861,8 @@ def xml_element(self, doc):
                 element.setAttribute(
                     "climatological", str(self.climatological)
                 )
-
+        if self.guess_coord:
+            element.setAttribute("guess_coord", str(self.guess_coord))
         if self.attributes:
             attributes_element = doc.createElement("attributes")
             for name in sorted(self.attributes.keys()):
@@ -1541,6 +1542,7 @@ def __init__(
         attributes=None,
         coord_system=None,
         climatological=False,
+        guess_coord=True,
     ):
         """
         Coordinate abstract base class. As of ``v3.0.0`` you **cannot** create an instance of :class:`Coord`.
@@ -1608,6 +1610,8 @@ def __init__(
         self.bounds = bounds
         self.climatological = climatological
 
+        self.guess_coord = guess_coord
+
     def copy(self, points=None, bounds=None):
         """
         Returns a copy of this coordinate.
@@ -1655,6 +1659,7 @@ def from_coord(cls, coord):
             "attributes": coord.attributes,
             "coord_system": copy.deepcopy(coord.coord_system),
             "climatological": coord.climatological,
+            "guess_coord": coord.guess_coord,
         }
         if issubclass(cls, DimCoord):
             # DimCoord introduces an extra constructor keyword.
@@ -1751,6 +1756,27 @@ def climatological(self, value):
 
         self._metadata_manager.climatological = value
 
+    @property
+    def guess_coord(self):
+        """
+        A boolean that controls whether guess_coord_axis acts on this
+        coordinate.
+
+        Defaults to True, and when set to False it will be skipped by
+        guess_coord_axis.
+        """
+        return self._metadata_manager.guess_coord
+
+    @guess_coord.setter
+    def guess_coord(self, value):
+        print(value)
+        if value is not True and value is not False:
+            emsg = "Guess_coord can only be set to True or False"
+            raise ValueError(emsg)
+        else:
+            pass
+        self._metadata_manager.guess_coord = value
+
     def lazy_points(self):
         """
         Return a lazy array representing the coord points.
@@ -2581,6 +2607,7 @@ def from_regular(
         coord_system=None,
         circular=False,
         climatological=False,
+        guess_coord=True,
         with_bounds=False,
     ):
         """
@@ -2630,6 +2657,7 @@ def from_regular(
             coord_system=coord_system,
             circular=circular,
             climatological=climatological,
+            guess_coord=guess_coord,
         )
 
     def __init__(
@@ -2644,6 +2672,7 @@ def __init__(
         coord_system=None,
         circular=False,
         climatological=False,
+        guess_coord=True,
     ):
         """
         Create a 1D, numeric, and strictly monotonic coordinate with **immutable** points and bounds.
@@ -2697,6 +2726,8 @@ def __init__(
             Will set to True when a climatological time axis is loaded
             from NetCDF.
             Always False if no bounds exist.
+        * guess_coord (bool):
+            When True: guess_coord will guess the coord, when False it won't.
 
         """
         # Configure the metadata manager.
@@ -2712,6 +2743,7 @@ def __init__(
             attributes=attributes,
             coord_system=coord_system,
             climatological=climatological,
+            guess_coord=guess_coord,
         )
 
         #: Whether the coordinate wraps by ``coord.units.modulus``.

lib/iris/tests/unit/coords/test_Coord.py

@@ -15,6 +15,7 @@
 
 import dask.array as da
 import numpy as np
+import pytest
 
 import iris
 from iris.coords import AuxCoord, Coord, DimCoord
@@ -1150,6 +1151,33 @@ def test_change_units(self):
         self.assertFalse(coord.climatological)
 
 
+@pytest.fixture
+def coord():
+    coord = iris.coords.DimCoord(points=(1, 2, 3, 4, 5))
+    return coord
+
+
+class Test_guess_coord:
+    def test_default(self, coord):
+        assert coord.guess_coord == True
+
+    def test_set_true(self, coord):
+        coord.guess_coord = True
+
+        assert coord.guess_coord == True
+
+    def test_set_false(self, coord):
+        coord.guess_coord = False
+
+        assert coord.guess_coord == False
+
+    def test_set_random_value(self, coord):
+        with pytest.raises(
+            ValueError, match=r"Guess_coord can only be set to True or False"
+        ):
+            coord.guess_coord = "foo"
+
+
 class Test___init____abstractmethod(tests.IrisTest):
     def test(self):
         emsg = (

lib/iris/tests/unit/util/test_guess_coord_axis.py

@@ -0,0 +1,50 @@
+# Copyright Iris contributors
+#
+# This file is part of Iris and is released under the LGPL license.
+# See COPYING and COPYING.LESSER in the root of the repository for full
+# licensing details.
+"""Test function :func:`iris.util.guess_coord_axis"""
+
+# Import iris.tests first so that some things can be initialised before
+# importing anything else.
+import iris.tests as tests  # isort:skip
+
+import numpy as np
+import pytest
+
+import iris.coords
+from iris.util import guess_coord_axis
+
+
+@pytest.fixture
+def coord():
+    coord = iris.coords.DimCoord(points=(1, 2, 3, 4, 5))
+    return coord
+
+
+class TestCoords:
+    def test_longitude(self, coord):
+        coord.standard_name = "longitude"
+
+        assert guess_coord_axis(coord) == "X"
+
+    def test_latitude(self, coord):
+        coord.standard_name = "latitude"
+
+        assert guess_coord_axis(coord) == "Y"
+
+    def test_pressure_units(self, coord):
+        coord.units = "hPa"
+
+        assert guess_coord_axis(coord) == "Z"
+
+    def test_time_units(self, coord):
+        coord.units = "days since 1970-01-01 00:00:00"
+
+        assert guess_coord_axis(coord) == "T"
+
+    def test_guess_coord(self, coord):
+        coord.standard_name = "longitude"
+        coord.guess_coord = False
+
+        assert guess_coord_axis(coord) == None

lib/iris/util.py

@@ -258,10 +258,17 @@ def guess_coord_axis(coord):
     This function maintains laziness when called; it does not realise data.
     See more at :doc:`/userguide/real_and_lazy_data`.
 
+    Can be skipped by setting the coordinate property of a coord guess_coord
+    to False.
+
     """
+
     axis = None
 
-    if coord.standard_name in (
+    if coord.guess_coord == False:
+        return None
+
+    elif coord.standard_name in (
         "longitude",
         "grid_longitude",
         "projection_x_coordinate",