Automatic info['nchan'] and info['ch_names']

The info object has two redundant fields: `nchan` and `ch_names`. They are
there as convenience fields. However, whenever the `chs` list is
updated, these fields need to be manually updated as well.

This PR makes these fields behave more like properties.

It does so by making `Info` a subclass of `collections.MutableMapping`, which allows
it to redefine `__setitem__` and `__getitem__` while retaining full
compatibility with the default Python dict.

The `nchan` field just maps to `len(info['chs'])`.

The `ch_names` field is a bit more tricky. From the outside, it behaves
as a mapping to `[ch['ch_name'] for ch in info['chs']]`. However, in order
not to generate a new list every time the field is accessed, the field
is an instance of `_ChannelNameList`.

The `_ChannelNameList` class is a subclass of `collections.Sequence`, thus
implementing a list that is read-only, but otherwise fully compatible
with a normal Python list. It overwrites the `__getitem(self, index)__` method to map
to `info['chs'][index]['ch_name']` on the fly.

The rest of the code is updated to no longer set the `nchan` and
`ch_names` fields of Info objects.

doc/whats_new.rst

@@ -47,6 +47,8 @@ API
 
     - Deprecated function :func:`mne.time_frequency.multitaper_psd` and replaced by :func:`mne.time_frequency.psd_multitaper` by `Chris Holdgraf`_
 
+    - The `'ch_names'` and `'nchan'` fields of the :class:`mne.io.Info` class are now read-only and automatically update to accommodate changes in the `'chs'` field, by `Marijn van Vliet`_
+
 .. _changes_0_11:
 
 Version 0.11

mne/channels/channels.py

@@ -651,7 +651,6 @@ def rename_channels(info, mapping):
 
     # do the reampping in info
     info['bads'] = bads
-    info['ch_names'] = ch_names
     for ch, ch_name in zip(info['chs'], ch_names):
         ch['ch_name'] = ch_name
     info._check_consistency()

mne/channels/layout.py

@@ -18,6 +18,7 @@
 from ..transforms import _polar_to_cartesian, _cartesian_to_sphere
 from ..io.pick import pick_types
 from ..io.constants import FIFF
+from ..io.meas_info import Info
 from ..utils import _clean_names
 from ..externals.six.moves import map
 
@@ -411,7 +412,7 @@ def find_layout(info, ch_type=None, exclude='bads'):
         layout_name = 'Vectorview-grad'
     elif ((has_eeg_coils_only and ch_type in [None, 'eeg']) or
           (has_eeg_coils_and_meg and ch_type == 'eeg')):
-        if not isinstance(info, dict):
+        if not isinstance(info, (dict, Info)):
             raise RuntimeError('Cannot make EEG layout, no measurement info '
                                'was passed to `find_layout`')
         return make_eeg_layout(info, exclude=exclude)

mne/channels/montage.py

@@ -619,7 +619,6 @@ def _set_montage(info, montage, update_ch_names=False):
     """
     if isinstance(montage, Montage):
         if update_ch_names:
-            info['ch_names'] = montage.ch_names
             info['chs'] = list()
             for ii, ch_name in enumerate(montage.ch_names):
                 ch_info = {'cal': 1., 'logno': ii + 1, 'scanno': ii + 1,
@@ -638,7 +637,6 @@ def _set_montage(info, montage, update_ch_names=False):
                 continue
 
             ch_idx = info['ch_names'].index(ch_name)
-            info['ch_names'][ch_idx] = ch_name
             info['chs'][ch_idx]['loc'] = np.r_[pos, [0.] * 9]
             sensors_found.append(ch_idx)
 

mne/channels/tests/test_layout.py

@@ -44,7 +44,6 @@
 
 test_info = _empty_info(1000)
 test_info.update({
-    'ch_names': ['ICA 001', 'ICA 002', 'EOG 061'],
     'chs': [{'cal': 1,
              'ch_name': 'ICA 001',
              'coil_type': 0,
@@ -81,7 +80,7 @@
              'scanno': 376,
              'unit': 107,
              'unit_mul': 0}],
-    'nchan': 3})
+})
 
 
 def test_io_layout_lout():
@@ -229,7 +228,6 @@ def test_find_layout():
     sample_info4 = copy.deepcopy(sample_info)
     for ii, name in enumerate(sample_info4['ch_names']):
         new = name.replace(' ', '')
-        sample_info4['ch_names'][ii] = new
         sample_info4['chs'][ii]['ch_name'] = new
 
     eegs = pick_types(sample_info, meg=False, eeg=True)

mne/evoked.py

@@ -198,7 +198,6 @@ def __init__(self, fname, condition=None, baseline=None, proj=True,
                                      'channel definitions are different')
 
                 info['chs'] = chs
-                info['nchan'] = nchan
                 logger.info('    Found channel information in evoked data. '
                             'nchan = %d' % nchan)
                 if sfreq > 0:

mne/forward/_field_interpolation.py

@@ -211,7 +211,6 @@ def _as_meg_type_evoked(evoked, ch_type='grad', mode='fast'):
     # change channel names to emphasize they contain interpolated data
     for ch in evoked.info['chs']:
         ch['ch_name'] += '_virtual'
-    evoked.info['ch_names'] = [ch['ch_name'] for ch in evoked.info['chs']]
 
     return evoked
 

mne/forward/_make_forward.py

@@ -423,10 +423,9 @@ def _prepare_for_forward(src, mri_head_t, info, bem, mindist, n_jobs,
                 mindist, overwrite, n_jobs, verbose]
     cmd = 'make_forward_solution(%s)' % (', '.join([str(a) for a in arg_list]))
     mri_id = dict(machid=np.zeros(2, np.int32), version=0, secs=0, usecs=0)
-    info = Info(nchan=info['nchan'], chs=info['chs'], comps=info['comps'],
-                ch_names=info['ch_names'], dev_head_t=info['dev_head_t'],
-                mri_file=trans, mri_id=mri_id, meas_file=info_extra,
-                meas_id=None, working_dir=os.getcwd(),
+    info = Info(chs=info['chs'], comps=info['comps'],
+                dev_head_t=info['dev_head_t'], mri_file=trans, mri_id=mri_id,
+                meas_file=info_extra, meas_id=None, working_dir=os.getcwd(),
                 command_line=cmd, bads=info['bads'], mri_head_t=mri_head_t)
     logger.info('')
 
@@ -549,13 +548,13 @@ def make_forward_solution(info, trans, src, bem, fname=None, meg=True,
     if fname is not None and op.isfile(fname) and not overwrite:
         raise IOError('file "%s" exists, consider using overwrite=True'
                       % fname)
-    if not isinstance(info, (dict, string_types)):
-        raise TypeError('info should be a dict or string')
+    if not isinstance(info, (Info, string_types)):
+        raise TypeError('info should be an instance of Info or string')
     if isinstance(info, string_types):
         info_extra = op.split(info)[1]
         info = read_info(info, verbose=False)
     else:
-        info_extra = 'info dict'
+        info_extra = 'instance of Info'
 
     # Report the setup
     logger.info('Source space                 : %s' % src)

mne/forward/forward.py

@@ -318,9 +318,6 @@ def _read_forward_meas_info(tree, fid):
             chs.append(tag.data)
     info['chs'] = chs
 
-    info['ch_names'] = [c['ch_name'] for c in chs]
-    info['nchan'] = len(chs)
-
     #   Get the MRI <-> head coordinate transformation
     tag = find_tag(fid, parent_mri, FIFF.FIFF_COORD_TRANS)
     coord_head = FIFF.FIFFV_COORD_HEAD

mne/io/brainvision/brainvision.py

@@ -328,10 +328,10 @@ def _get_vhdr_info(vhdr_fname, eog, misc, scale, montage):
     fmt = _fmt_dict[fmt]
 
     # load channel labels
-    info['nchan'] = cfg.getint('Common Infos', 'NumberOfChannels') + 1
-    ch_names = [''] * info['nchan']
-    cals = np.empty(info['nchan'])
-    ranges = np.empty(info['nchan'])
+    nchan = cfg.getint('Common Infos', 'NumberOfChannels') + 1
+    ch_names = [''] * nchan
+    cals = np.empty(nchan)
+    ranges = np.empty(nchan)
     cals.fill(np.nan)
     ch_dict = dict()
     for chan, props in cfg.items('Channel Infos'):
@@ -437,13 +437,12 @@ def _get_vhdr_info(vhdr_fname, eog, misc, scale, montage):
     # Creates a list of dicts of eeg channels for raw.info
     logger.info('Setting channel info structure...')
     info['chs'] = []
-    info['ch_names'] = ch_names
     for idx, ch_name in enumerate(ch_names):
-        if ch_name in eog or idx in eog or idx - info['nchan'] in eog:
+        if ch_name in eog or idx in eog or idx - nchan in eog:
             kind = FIFF.FIFFV_EOG_CH
             coil_type = FIFF.FIFFV_COIL_NONE
             unit = FIFF.FIFF_UNIT_V
-        elif ch_name in misc or idx in misc or idx - info['nchan'] in misc:
+        elif ch_name in misc or idx in misc or idx - nchan in misc:
             kind = FIFF.FIFFV_MISC_CH
             coil_type = FIFF.FIFFV_COIL_NONE
             unit = FIFF.FIFF_UNIT_V

mne/io/bti/bti.py

@@ -1120,7 +1120,6 @@ def _get_bti_info(pdf_fname, config_fname, head_shape_fname, rotation_x,
     info['buffer_size_sec'] = 1.  # reasonable default for writing
     date = bti_info['processes'][0]['timestamp']
     info['meas_date'] = [date, 0]
-    info['nchan'] = len(bti_info['chs'])
 
     # browse processing info for filter specs.
     hp, lp = info['highpass'], info['lowpass']
@@ -1211,7 +1210,6 @@ def _get_bti_info(pdf_fname, config_fname, head_shape_fname, rotation_x,
         chs.append(chan_info)
 
     info['chs'] = chs
-    info['ch_names'] = neuromag_ch_names if rename_channels else bti_ch_names
 
     if head_shape_fname:
         logger.info('... Reading digitization points from %s' %

mne/io/ctf/info.py

@@ -389,13 +389,11 @@ def _compose_meas_info(res4, coils, trans, eeg):
         if trans['t_ctf_head_head'] is not None:
             info['ctf_head_t'] = trans['t_ctf_head_head']
     info['chs'] = _convert_channel_info(res4, trans, eeg is None)
-    info['nchan'] = len(info['chs'])
     info['comps'] = _convert_comp_data(res4)
     if eeg is None:
         # Pick EEG locations from chan info if not read from a separate file
         eeg = _pick_eeg_pos(info)
     _add_eeg_pos(eeg, trans, info)
-    info['ch_names'] = [ch['ch_name'] for ch in info['chs']]
     logger.info('    Measurement info composed.')
     info._check_consistency()
     return info

mne/io/edf/edf.py

@@ -430,9 +430,7 @@ def _get_edf_info(fname, stim_channel, annot, annotmap, eog, misc, preload):
     info = _empty_info(sfreq)
     info['filename'] = fname
     info['meas_date'] = calendar.timegm(date.utctimetuple())
-    info['nchan'] = nchan
     info['chs'] = chs
-    info['ch_names'] = ch_names
 
     if highpass.size == 0:
         pass

mne/io/eeglab/eeglab.py

@@ -63,7 +63,6 @@ def _get_info(eeg, montage, eog=()):
     """Get measurement info.
     """
     info = _empty_info(sfreq=eeg.srate)
-    info['nchan'] = eeg.nbchan
 
     # add the ch_names and info['chs'][idx]['loc']
     path = None

mne/io/egi/egi.py

@@ -255,8 +255,7 @@ def __init__(self, input_fname, montage=None, eog=None, misc=None,
         ch_names.extend(list(egi_info['event_codes']))
         if self._new_trigger is not None:
             ch_names.append('STI 014')  # our new_trigger
-        info['nchan'] = nchan = len(ch_names)
-        info['ch_names'] = ch_names
+        nchan = len(ch_names)
         for ii, ch_name in enumerate(ch_names):
             ch_info = {
                 'cal': cal, 'logno': ii + 1, 'scanno': ii + 1, 'range': 1.0,

mne/io/fiff/tests/test_raw_fiff.py

@@ -1019,8 +1019,10 @@ def test_add_channels():
     raw_meg = raw.pick_types(meg=True, eeg=False, copy=True)
     raw_stim = raw.pick_types(meg=False, eeg=False, stim=True, copy=True)
     raw_new = raw_meg.add_channels([raw_eeg, raw_stim], copy=True)
-    assert_true(all(ch in raw_new.ch_names
-                    for ch in raw_stim.ch_names + raw_meg.ch_names))
+    assert_true(
+        all(ch in raw_new.ch_names
+            for ch in list(raw_stim.ch_names) + list(raw_meg.ch_names))
+    )
     raw_new = raw_meg.add_channels([raw_eeg], copy=True)
 
     assert_true(ch in raw_new.ch_names for ch in raw.ch_names)

mne/io/kit/kit.py

@@ -195,12 +195,12 @@ def _set_stimchannels(self, info, stim, stim_code):
                                  % (np.max(stim),
                                     self._raw_extras[0]['nchan']))
             # modify info
-            info['nchan'] = self._raw_extras[0]['nchan'] + 1
+            nchan = self._raw_extras[0]['nchan'] + 1
             ch_name = 'STI 014'
             chan_info = {}
             chan_info['cal'] = KIT.CALIB_FACTOR
-            chan_info['logno'] = info['nchan']
-            chan_info['scanno'] = info['nchan']
+            chan_info['logno'] = nchan
+            chan_info['scanno'] = nchan
             chan_info['range'] = 1.0
             chan_info['unit'] = FIFF.FIFF_UNIT_NONE
             chan_info['unit_mul'] = 0
@@ -209,7 +209,6 @@ def _set_stimchannels(self, info, stim, stim_code):
             chan_info['loc'] = np.zeros(12)
             chan_info['kind'] = FIFF.FIFFV_STIM_CH
             info['chs'].append(chan_info)
-            info['ch_names'].append(ch_name)
         if self.preload:
             err = "Can't change stim channel after preloading data"
             raise NotImplementedError(err)
@@ -661,7 +660,7 @@ def get_kit_info(rawfile):
         info = _empty_info(float(sqd['sfreq']))
         info.update(meas_date=int(time.time()), lowpass=sqd['lowpass'],
                     highpass=sqd['highpass'], filename=rawfile,
-                    nchan=sqd['nchan'], buffer_size_sec=1.)
+                    buffer_size_sec=1.)
 
         # Creates a list of dicts of meg channels for raw.info
         logger.info('Setting channel info structure...')
@@ -738,8 +737,6 @@ def get_kit_info(rawfile):
             chan_info['kind'] = FIFF.FIFFV_MISC_CH
             info['chs'].append(chan_info)
 
-        info['ch_names'] = ch_names['MEG'] + ch_names['MISC']
-
     return info, sqd