From 21489d572fdb500fae5852a839a09afc7f89890f Mon Sep 17 00:00:00 2001
From: Elias Sadek <elias.sadek@metoffice.gov.uk>
Date: Wed, 18 Dec 2024 12:49:30 +0000
Subject: [PATCH] added in exceptions, not tested

---
 lib/iris/cube.py       | 24 +++++++++++++++++++++++-
 lib/iris/exceptions.py | 11 +++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/lib/iris/cube.py b/lib/iris/cube.py
index fca5539135..e5d0573b0d 100644
--- a/lib/iris/cube.py
+++ b/lib/iris/cube.py
@@ -174,6 +174,8 @@ def _assert_is_cube(obj):
         if not hasattr(obj, "add_aux_coord"):
             msg = r"Object {obj} cannot be put in a cubelist, as it is not a Cube."
             raise ValueError(msg)
+        elif obj.is_dataless():
+            raise iris.exceptions.DatalessError("CubeList")
 
     def _repr_html_(self):
         from iris.experimental.representation import CubeListRepresentation
@@ -1479,6 +1481,8 @@ def convert_units(self, unit: str | Unit) -> None:
 
         """
         # If the cube has units convert the data.
+        if self.is_dataless():
+            raise iris.exceptions.DatalessError("convert_units")
         if self.units.is_unknown():
             raise iris.exceptions.UnitConversionError(
                 "Cannot convert from unknown units. "
@@ -3105,6 +3109,8 @@ def subset(self, coord: AuxCoord | DimCoord) -> Cube | None:
         whole cube is returned. As such, the operation is not strict.
 
         """
+        if self.is_dataless():
+            raise iris.exceptions.DatalessError("subset")
         if not isinstance(coord, iris.coords.Coord):
             raise ValueError("coord_to_extract must be a valid Coord.")
 
@@ -3226,6 +3232,8 @@ def intersection(self, *args, **kwargs) -> Cube:
             which intersects with the requested coordinate intervals.
 
         """
+        if self.is_dataless():
+            raise iris.exceptions.DatalessError("intersection")
         result = self
         ignore_bounds = kwargs.pop("ignore_bounds", False)
         threshold = kwargs.pop("threshold", 0)
@@ -3750,6 +3758,9 @@ def slices(
             dimension index.
 
         """  # noqa: D214, D406, D407, D410, D411
+        if self.is_dataless():
+            raise iris.exceptions.DatalessError("slices")
+
         if not isinstance(ordered, bool):
             raise TypeError("'ordered' argument to slices must be boolean.")
 
@@ -3837,7 +3848,8 @@ def transpose(self, new_order: list[int] | None = None) -> None:
 
         # Transpose the data payload.
         dm = self._data_manager
-        data = dm.core_data().transpose(new_order)
+        if not self.is_dataless():
+            data = dm.core_data().transpose(new_order)
         self._data_manager = DataManager(data)
 
         dim_mapping = {src: dest for dest, src in enumerate(new_order)}
@@ -4325,6 +4337,8 @@ def collapsed(
                 cube.collapsed(['latitude', 'longitude'],
                                iris.analysis.VARIANCE)
         """
+        if self.is_dataless():
+            raise iris.exceptions.DatalessError("collapsed")
         # Update weights kwargs (if necessary) to handle different types of
         # weights
         weights_info = None
@@ -4545,6 +4559,8 @@ def aggregated_by(
                     STASH                       m01s00i024
 
         """
+        if self.is_dataless():
+            raise iris.exceptions.DatalessError("aggregated_by")
         # Update weights kwargs (if necessary) to handle different types of
         # weights
         weights_info = None
@@ -4844,6 +4860,8 @@ def rolling_window(
         """  # noqa: D214, D406, D407, D410, D411
         # Update weights kwargs (if necessary) to handle different types of
         # weights
+        if self.is_dataless():
+            raise iris.exceptions.DatalessError("rolling_window")
         weights_info = None
         if kwargs.get("weights") is not None:
             weights_info = _Weights(kwargs["weights"], self)
@@ -5049,6 +5067,8 @@ def interpolate(
             True
 
         """
+        if self.is_dataless():
+            raise iris.exceptions.DatalessError("interoplate")
         coords, points = zip(*sample_points)
         interp = scheme.interpolator(self, coords)  # type: ignore[arg-type]
         return interp(points, collapse_scalar=collapse_scalar)
@@ -5094,6 +5114,8 @@ def regrid(self, grid: Cube, scheme: iris.analysis.RegriddingScheme) -> Cube:
             this function is not applicable.
 
         """
+        if self.is_dataless():
+            raise iris.exceptions.DatalessError("regrid")
         regridder = scheme.regridder(self, grid)
         return regridder(self)
 
diff --git a/lib/iris/exceptions.py b/lib/iris/exceptions.py
index d6d2084d3c..450afce3a6 100644
--- a/lib/iris/exceptions.py
+++ b/lib/iris/exceptions.py
@@ -161,3 +161,14 @@ class CannotAddError(ValueError):
     """Raised when an object (e.g. coord) cannot be added to a :class:`~iris.cube.Cube`."""
 
     pass
+
+
+class DatalessError(ValueError):
+    """Raised when an method cannot be performed on a dataless :class:`~iris.cube.Cube`."""
+
+    def __str__(self):
+        msg = (
+            "Dataless cubes are still early in implementation, and dataless {} "
+            "operations are not currently supported."
+        )
+        return msg.format(super().__str__())