Preserve planar contour on ProbeGroup slicing and clarify ambiguous select_contacts errors

src/probeinterface/probegroup.py

@@ -427,6 +427,11 @@ def get_slice(self, selection: np.ndarray[bool | int]) -> "ProbeGroup":
                 if k not in new_probe.annotations:
                     new_probe.annotate(**{k: orig_probe.annotations[k]})
 
+            # probe_planar_contour is a probe-level attribute, not part of the to_numpy dtype,
+            # so from_numpy cannot restore it; copy it over explicitly.
+            if orig_probe.probe_planar_contour is not None and new_probe.probe_planar_contour is None:
+                new_probe.set_planar_contour(orig_probe.probe_planar_contour)
+
         return sliced_probe_group
 
     def select_probes(self, probe_ids: str | np.ndarray | list) -> "ProbeGroup":
@@ -494,6 +499,21 @@ def select_contacts(
                     f"contact_ids must be unique, but {duplicated.tolist()} appear more than once. "
                     "If the same contact id is on multiple probes, use probe_ids to disambiguate."
                 )
+            # each requested contact id must live on exactly one probe; collect every
+            # ambiguous one so the user can disambiguate them all at once
+            ambiguous = {}
+            for contact_id in contact_ids:
+                probes_for_id = np.unique(all_probe_ids[all_contact_ids == contact_id]).tolist()
+                if len(probes_for_id) > 1:
+                    ambiguous[str(contact_id)] = probes_for_id
+            if ambiguous:
+                ambiguity_lines = "\n".join(
+                    f'"{contact_id}" lives on probes {probes}' for contact_id, probes in ambiguous.items()
+                )
+                message = f"""\
+Some contact ids are ambiguous because they live on multiple probes; pass probe_ids to disambiguate which probe each belongs to:
+{ambiguity_lines}"""
+                raise ValueError(message)
             probe_ids = [None] * len(contact_ids)
         else:
             if len(probe_ids) != len(contact_ids):

tests/test_probegroup.py

@@ -675,6 +675,49 @@ def test_add_probe_default_id_with_non_numeric_ids():
     assert pg.probe_ids == ["left", "right", "0"]
 
 
+def test_select_contacts_ambiguous_id_message_points_to_probe_ids():
+    """
+    When a contact id exists on several probes and no probe_ids are given, the
+    error must guide the user to pass probe_ids rather than claim it cannot happen.
+    """
+    pg = _probegroup_with_contact_ids(unique=False)
+    expected_error = """Some contact ids are ambiguous because they live on multiple probes; pass probe_ids to disambiguate which probe each belongs to:
+"c0" lives on probes ['0', '1', '2']"""
+    with pytest.raises(ValueError) as exc_info:
+        pg.select_contacts(["c0"])
+    assert str(exc_info.value) == expected_error
+
+
+def test_select_contacts_reports_all_ambiguous_ids_at_once():
+    """
+    When several requested contact ids are ambiguous, the error lists all of them
+    (with the probes each lives on) rather than failing on the first one.
+    """
+    pg = _probegroup_with_contact_ids(unique=False)
+    expected_error = """Some contact ids are ambiguous because they live on multiple probes; pass probe_ids to disambiguate which probe each belongs to:
+"c0" lives on probes ['0', '1', '2']
+"c1" lives on probes ['0', '1', '2']"""
+    with pytest.raises(ValueError) as exc_info:
+        pg.select_contacts(["c0", "c1"])
+    assert str(exc_info.value) == expected_error
+
+
+def test_get_slice_preserves_planar_contour():
+    """
+    probe_planar_contour is a probe-level attribute (not part of the to_numpy
+    dtype), so get_slice must copy it over explicitly instead of losing it.
+    """
+    pg = ProbeGroup()
+    probe = generate_dummy_probe()
+    contour = [[-10, -10], [-10, 100], [50, 120], [50, -10]]
+    probe.set_planar_contour(contour)
+    pg.add_probe(probe)
+
+    sub = pg.get_slice(np.array([0, 1, 2]))
+    assert sub.probes[0].probe_planar_contour is not None
+    np.testing.assert_array_equal(sub.probes[0].probe_planar_contour, contour)
+
+
 if __name__ == "__main__":
     probegroup = _make_probegroup()