Fix bug in cf.Field.match_by_construct

Changelog.rst

@@ -1,3 +1,13 @@
+version 3.15.4
+--------------
+
+**2023-??-??**
+
+* Fix bug in `cf.Field.match_by_construct` that always returned True for
+  1-d constructs whose axis is not in the data, even when the
+  criterion was not matched
+  (https://github.com/NCAS-CMS/cf-python/issues/691)
+
 version 3.15.3
 --------------
 
@@ -54,7 +64,7 @@ version 3.15.1
   (https://github.com/NCAS-CMS/cf-python/pull/654)
 * Fix `set_data` when the units are invalid
   (https://github.com/NCAS-CMS/cf-python/pull/646)
-* Fix `cf.Field.laplacian_xy`, cf.Field.grad_xy`, `cf.curl_xy` and
+* Fix `cf.Field.laplacian_xy`, `cf.Field.grad_xy`, `cf.curl_xy` and
   `cf.div_xy` to work in cases when the dimension coordinates are
   missing standard names
   (https://github.com/NCAS-CMS/cf-python/pull/643)

cf/field.py

@@ -10081,7 +10081,24 @@ def indices(self, *mode, **kwargs):
             indices = []
 
         # Add the indices that apply to the field's data dimensions
-        indices.extend([domain_indices["indices"][axis] for axis in data_axes])
+        axis_indices = domain_indices["indices"]
+        indices.extend([axis_indices[axis] for axis in data_axes])
+
+        # Check that there are no invalid indices for size 1 axes not
+        # spanned by the data
+        if len(axis_indices) > len(data_axes):
+            for axis, index in axis_indices.items():
+                if axis in data_axes or index == slice(None):
+                    continue
+
+                import dask.array as da
+
+                shape = da.from_array([0])[index].compute_chunk_sizes().shape
+                if 0 in shape:
+                    raise IndexError(
+                        "Can't create size 0 indices for the size 1 "
+                        f"{self.constructs.domain_axis_identity(axis)!r} axis"
+                    )
 
         return tuple(indices)
 

cf/mixin/fielddomain.py

@@ -344,7 +344,8 @@ def _indices(self, mode, data_axes, ancillary_mask, kwargs):
 
             if debug:
                 logger.debug(
-                    f"  item_axes    = {item_axes!r}\n  keys         = {keys!r}"
+                    f"  item_axes    = {item_axes!r}\n"
+                    f"  keys         = {keys!r}"
                 )  # pragma: no cover
 
             if n_axes == 1:
@@ -369,9 +370,9 @@ def _indices(self, mode, data_axes, ancillary_mask, kwargs):
                 if isinstance(value, (list, slice, tuple, np.ndarray)):
                     # 1-d CASE 1: Value is already an index, e.g. [0],
                     #             [7,4,2], slice(0,4,2),
-                    #             numpy.array([2,4,7]), [True, False,
-                    #             True]
-
+                    #             numpy.array([2,4,7]),
+                    #             [True,False,True]
+                    index = value
                     if debug:
                         logger.debug("  1-d CASE 1:")  # pragma: no cover
 
@@ -475,7 +476,7 @@ def _indices(self, mode, data_axes, ancillary_mask, kwargs):
 
                 if debug:
                     logger.debug(
-                        f"  index        = {index}\n  ind          = {ind}"
+                        f"    index      = {index}\n    ind        = {ind}"
                     )  # pragma: no cover
 
                 # Put the index into the correct place in the list of

cf/test/test_Field.py

@@ -1637,7 +1637,9 @@ def test_Field_match(self):
         self.assertFalse(g.match_by_naxes(3))
         self.assertFalse(g.match_by_naxes(99, 88))
 
-        # Match by construct
+    def test_Field_match_by_construct(self):
+        f = self.f.copy()
+
         for OR in (True, False):
             self.assertTrue(f.match_by_construct(OR=OR))
             self.assertTrue(f.match_by_construct("X", OR=OR))
@@ -1673,6 +1675,11 @@ def test_Field_match(self):
             )
         )
 
+        # Check match for size 1 axes that are not spanned by the data
+        f = cf.example_field(0)
+        self.assertTrue(f.match_by_construct(T=cf.dt("2019-01-01")))
+        self.assertFalse(f.match_by_construct(T=cf.dt("9876-12-31")))
+
     def test_Field_autocyclic(self):
         f = self.f.copy()