Add _on_missing functionality to UpdateChannelsMixin

doc/changes/latest.inc

@@ -32,6 +32,7 @@ Enhancements
 - Add ``starting_affine`` keyword argument to :func:`mne.transforms.compute_volume_registration` to initialize an alignment with an affine (:gh:`11020` by `Alex Rockhill`_)
 - The ``trans`` parameter in :func:`mne.make_field_map` now accepts a :class:`~pathlib.Path` object, and uses standardised loading logic (:gh:`10784` by :newcontrib:`Andrew Quinn`)
 - Allow :func:`mne.beamformer.make_dics` to take ``pick_ori='vector'`` to compute vector source estimates (:gh:`19080` by `Alex Rockhill`_)
+- Add ``on_missing`` functionality to all of our classes that have a ``drop_channels`` method, to control what happens when channel names are not in the object (:gh:`11077` by `Andrew Quinn`_)
 
 Bugs
 ~~~~

mne/channels/channels.py

@@ -24,7 +24,8 @@
 from ..defaults import HEAD_SIZE_DEFAULT, _handle_default
 from ..utils import (verbose, logger, warn,
                      _check_preload, _validate_type, fill_doc, _check_option,
-                     _get_stim_channel, _check_fname, _check_dict_keys)
+                     _get_stim_channel, _check_fname, _check_dict_keys,
+                     _on_missing)
 from ..io.constants import FIFF
 from ..io.meas_info import (anonymize_info, Info, MontageMixin, create_info,
                             _rename_comps)
@@ -735,13 +736,15 @@ def reorder_channels(self, ch_names):
             idx.append(ii)
         return self._pick_drop_channels(idx)
 
-    def drop_channels(self, ch_names):
+    @fill_doc
+    def drop_channels(self, ch_names, on_missing='raise'):
         """Drop channel(s).
 
         Parameters
         ----------
         ch_names : iterable or str
             Iterable (e.g. list) of channel name(s) or channel name to remove.
+        %(on_missing_ch_names)s
 
         Returns
         -------
@@ -774,7 +777,7 @@ def drop_channels(self, ch_names):
         missing = [ch for ch in ch_names if ch not in self.ch_names]
         if len(missing) > 0:
             msg = "Channel(s) {0} not found, nothing dropped."
-            raise ValueError(msg.format(", ".join(missing)))
+            _on_missing(on_missing, msg.format(", ".join(missing)))
 
         bad_idx = [self.ch_names.index(ch) for ch in ch_names
                    if ch in self.ch_names]

mne/channels/tests/test_channels.py

@@ -449,6 +449,16 @@ def test_drop_channels():
     pytest.raises(ValueError, raw.drop_channels, ["MEG 0111", 5])
     pytest.raises(ValueError, raw.drop_channels, 5)  # must be list or str
 
+    # by default, drop channels raises a ValueError if a channel can't be found
+    m_chs = ["MEG 0111", "MEG blahblah"]
+    with pytest.raises(ValueError, match='not found, nothing dropped'):
+        raw.drop_channels(m_chs)
+    # ...but this can be turned to a warning
+    with pytest.raises(RuntimeWarning, match='not found, nothing dropped'):
+        raw.drop_channels(m_chs, on_missing='warn')
+    # ...or ignored altogether
+    raw.drop_channels(m_chs, on_missing='ignore')
+
 
 def test_pick_channels():
     """Test if picking channels works with various arguments."""