ENH: improved error message on invalid getitem key (closes #1101)

doc/source/changes/version_0_34_3.rst.inc

@@ -7,6 +7,40 @@ New features
 * added support for Python 3.12 (closes :issue:`1109`).
 
 
+Miscellaneous improvements
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+* improved the error message when selecting several labels at the same time and some of them were wrong.
+  In that case, it was hard to know which labels were wrong. This was especially annoying if the axis was long and
+  thus not shown in its entirety in the error message. For example, given the following array: ::
+
+    >>> arr = la.ndtest('a=a0,a1;b=b0..b2,b4..b7')
+    >>> arr
+    a\b  b0  b1  b2  b4  b5  b6  b7
+     a0   0   1   2   3   4   5   6
+     a1   7   8   9  10  11  12  13
+
+  This code: ::
+
+    >>> arr['b0,b2,b3,b7']
+
+  used to produce the following error: ::
+
+    ValueError: 'b0,b2,b3,b7' is not a valid label for any axis:
+     a [2]: 'a0' 'a1'
+     b [7]: 'b0' 'b1' 'b2' ... 'b5' 'b6' 'b7'
+
+  which did not contain enough information to determine the problem was with 'b3'. It now produces this instead: ::
+
+    ValueError: 'b0,b2,b3,b7' is not a valid subset for any axis:
+     a [2]: 'a0' 'a1'
+     b [7]: 'b0' 'b1' 'b2' ... 'b5' 'b6' 'b7'
+    Some of those labels are valid though:
+     * axis 'b' contains 3 out of 4 labels (missing labels: 'b3')
+
+  Closes :issue:`1101`.
+
+
 Fixes
 ^^^^^
 

larray/core/axis.py

@@ -2681,7 +2681,38 @@ def _translate_nice_key(self, axis_key):
             except KeyError:
                 continue
         if not valid_axes:
-            raise ValueError(f"{axis_key!r} is not a valid label for any axis:\n{self._axes_summary()}")
+            # if the key has several labels
+            nicer_key = _to_key(axis_key)
+            sequence_types = (tuple, list, np.ndarray, ABCArray)
+            if (isinstance(nicer_key, sequence_types) or
+                (isinstance(nicer_key, Group) and isinstance(nicer_key.key, sequence_types))):
+
+                # we use a different "base" message in this case (because axis_key is not really a *label*)
+                msg = f"{axis_key!r} is not a valid subset for any axis:\n{self._axes_summary()}"
+
+                # ... and check for partial matches
+                if isinstance(nicer_key, Group):
+                    nicer_key = nicer_key.eval()
+                key_label_set = set(nicer_key)
+                partial_matches = {}
+                for axis in self:
+                    missing_labels = key_label_set - set(axis.labels)
+                    if missing_labels < key_label_set:
+                        partial_matches[axis] = missing_labels
+
+                if partial_matches:
+                    partial_matches_str = '\n'.join(
+                        f" * axis '{self.axis_id(axis)}' contains {len(key_label_set) - len(missing_labels)}"
+                        f' out of {len(key_label_set)}'
+                        f' labels (missing labels: {", ".join(repr(label) for label in missing_labels)})'
+                        for axis, missing_labels in partial_matches.items()
+                    )
+                    msg += f"\nSome of those labels are valid though:\n{partial_matches_str}"
+            else:
+                # we have single label
+                msg = f"{axis_key!r} is not a valid label for any axis:\n{self._axes_summary()}"
+
+            raise ValueError(msg)
         elif len(valid_axes) > 1:
             raise ValueError(f'{axis_key!r} is ambiguous, it is valid in the following axes:\n'
                              f'{self._axes_summary(valid_axes)}')

larray/tests/test_array.py

@@ -664,7 +664,7 @@ def test_getitem_guess_axis(array):
         _ = array[[1, 2], 999]
 
     # key with invalid label list (ie list of labels not found on any axis)
-    with must_raise(ValueError, """[998, 999] is not a valid label for any axis:
+    with must_raise(ValueError, """[998, 999] is not a valid subset for any axis:
  a [19]: 0 1 2 ... 16 17 18
  b [12]: 'b0' 'b1' 'b2' ... 'b10' 'b11' 'b3'
  c [2]: 'c0' 'c1'
@@ -678,11 +678,13 @@ def test_getitem_guess_axis(array):
                                 "7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18"):
         _ = array[[1, 2], [3, 999]]
 
-    with must_raise(ValueError, """[999, 4] is not a valid label for any axis:
+    with must_raise(ValueError, """[999, 4] is not a valid subset for any axis:
  a [19]: 0 1 2 ... 16 17 18
  b [12]: 'b0' 'b1' 'b2' ... 'b10' 'b11' 'b3'
  c [2]: 'c0' 'c1'
- d [6]: 'd1' 'd2' 'd3' 'd4' 'd5' 'd6'"""):
+ d [6]: 'd1' 'd2' 'd3' 'd4' 'd5' 'd6'
+Some of those labels are valid though:
+ * axis 'a' contains 1 out of 2 labels (missing labels: 999)"""):
         _ = array[[1, 2], [999, 4]]
 
     # ambiguous key