From 7901bbc2fb2b1d84dba73757a66bddc8c08a8d0d Mon Sep 17 00:00:00 2001
From: Elias Sadek <elias.sadek@metoffice.gov.uk>
Date: Thu, 18 Dec 2025 14:32:30 +0000
Subject: [PATCH] refactored DatalessError

---
 lib/iris/_lazy_data.py | 2 +-
 lib/iris/cube.py       | 6 ++++--
 lib/iris/exceptions.py | 9 ++-------
 3 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/lib/iris/_lazy_data.py b/lib/iris/_lazy_data.py
index c74da78d6b..2de7f8c5ac 100644
--- a/lib/iris/_lazy_data.py
+++ b/lib/iris/_lazy_data.py
@@ -370,7 +370,7 @@ def _co_realise_lazy_arrays(arrays):
         if real_out is not None:
             real_out = np.asanyarray(real_out)
         else:
-            raise iris.exceptions.DatalessError("realising")
+            raise iris.exceptions.DatalessError("Data is None; cannot be realised.")
         if isinstance(real_out, ma.core.MaskedConstant):
             # Convert any masked constants into NumPy masked arrays.
             # NOTE: in this case, also apply the original lazy-array dtype, as
diff --git a/lib/iris/cube.py b/lib/iris/cube.py
index 7d077581e1..a68e9d7599 100644
--- a/lib/iris/cube.py
+++ b/lib/iris/cube.py
@@ -5374,7 +5374,9 @@ def interpolate(
 
         """
         if self.is_dataless():
-            raise iris.exceptions.DatalessError("interpolate")
+            raise iris.exceptions.DatalessError(
+                "Dataless cubes cannot be interpolated."
+            )
         coords, points = zip(*sample_points)
         interp = scheme.interpolator(self, coords)  # type: ignore[arg-type]
         return interp(points, collapse_scalar=collapse_scalar)
@@ -5421,7 +5423,7 @@ def regrid(self, grid: Cube, scheme: iris.analysis.RegriddingScheme) -> Cube:
 
         """
         if self.is_dataless():
-            raise iris.exceptions.DatalessError("regrid")
+            raise iris.exceptions.DatalessError("Dataless cubes cannot be regridded.")
         regridder = scheme.regridder(self, grid)
         return regridder(self)
 
diff --git a/lib/iris/exceptions.py b/lib/iris/exceptions.py
index 2ac0e35dc4..56e220faf9 100644
--- a/lib/iris/exceptions.py
+++ b/lib/iris/exceptions.py
@@ -170,14 +170,9 @@ class CannotAddError(ValueError):
 
 
 class DatalessError(ValueError):
-    """Raised when an method cannot be performed on a dataless :class:`~iris.cube.Cube`."""
+    """Raised when a 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__())
+    pass
 
 
 class CFParseError(IrisError):