ENH: Add Forward.save and hdf5 support

doc/changes/devel.rst

@@ -33,6 +33,7 @@ Enhancements
 - Add helpful error messages when using methods on empty :class:`mne.Epochs`-objects (:gh:`11306` by `Martin Schulz`_)
 - Add inferring EEGLAB files' montage unit automatically based on estimated head radius using :func:`read_raw_eeglab(..., montage_units="auto") <mne.io.read_raw_eeglab>` (:gh:`11925` by `Jack Zhang`_, :gh:`11951` by `Eric Larson`_)
 - Add :class:`~mne.time_frequency.EpochsSpectrumArray` and :class:`~mne.time_frequency.SpectrumArray` to support creating power spectra from :class:`NumPy array <numpy.ndarray>` data (:gh:`11803` by `Alex Rockhill`_)
+- Add support for writing forward solutions to HDF5 and convenience function :meth:`mne.forward.Forward.save` (:gh:`12036` by `Eric Larson`_)
 - Refactored internals of :func:`mne.read_annotations` (:gh:`11964` by `Paul Roujansky`_)
 - Enhance :func:`~mne.viz.plot_evoked_field` with a GUI that has controls for time, colormap, and contour lines (:gh:`11942` by `Marijn van Vliet`_)
 

mne/_fiff/meas_info.py

@@ -80,6 +80,7 @@
     _check_on_missing,
     fill_doc,
     _check_fname,
+    check_fname,
     repr_html,
 )
 from ._digitization import (
@@ -2006,6 +2007,8 @@ def read_info(fname, verbose=None):
     -------
     %(info_not_none)s
     """
+    check_fname(fname, "Info", (".fif", ".fif.gz"))
+    fname = _check_fname(fname, must_exist=True, overwrite="read")
     f, tree, _ = fiff_open(fname)
     with f as fid:
         info = read_meas_info(fid, tree)[0]

mne/_fiff/tests/test_meas_info.py

@@ -345,6 +345,14 @@ def test_read_write_info(tmp_path):
         write_info(fname, info)
 
 
+@testing.requires_testing_data
+def test_dir_warning():
+    """Test that trying to read a bad filename emits a warning before an error."""
+    with pytest.raises(OSError, match="directory"):
+        with pytest.warns(RuntimeWarning, match="foo"):
+            read_info(ctf_fname)
+
+
 def test_io_dig_points(tmp_path):
     """Test Writing for dig files."""
     dest = tmp_path / "test.txt"

mne/forward/forward.py

@@ -81,6 +81,7 @@
     _stamp_to_dt,
     _on_missing,
     repr_html,
+    _import_h5io_funcs,
 )
 from ..label import Label
 
@@ -165,6 +166,18 @@ def copy(self):
         """Copy the Forward instance."""
         return Forward(deepcopy(self))
 
+    @verbose
+    def save(self, fname, *, overwrite=False, verbose=None):
+        """Save the forward solution.
+
+        Parameters
+        ----------
+        %(fname_fwd)s
+        %(overwrite)s
+        %(verbose)s
+        """
+        write_forward_solution(fname, self, overwrite=overwrite)
+
     def _get_src_type_and_ori_for_repr(self):
         src_types = np.array([src["type"] for src in self["src"]])
 
@@ -520,7 +533,8 @@ def read_forward_solution(fname, include=(), exclude=(), *, ordered=None, verbos
     Parameters
     ----------
     fname : path-like
-        The file name, which should end with ``-fwd.fif`` or ``-fwd.fif.gz``.
+        The file name, which should end with ``-fwd.fif``, ``-fwd.fif.gz``,
+        ``_fwd.fif``, ``_fwd.fif.gz``, ``-fwd.h5``, or ``_fwd.h5``.
     include : list, optional
         List of names of channels to include. If empty all channels
         are included.
@@ -554,11 +568,15 @@ def read_forward_solution(fname, include=(), exclude=(), *, ordered=None, verbos
     forward solution with :func:`read_forward_solution`.
     """
     check_fname(
-        fname, "forward", ("-fwd.fif", "-fwd.fif.gz", "_fwd.fif", "_fwd.fif.gz")
+        fname,
+        "forward",
+        ("-fwd.fif", "-fwd.fif.gz", "_fwd.fif", "_fwd.fif.gz", "-fwd.h5", "_fwd.h5"),
     )
     fname = _check_fname(fname=fname, must_exist=True, overwrite="read")
     #   Open the file, create directory
     logger.info("Reading forward solution from %s..." % fname)
+    if fname.suffix == ".h5":
+        return _read_forward_hdf5(fname)
     f, tree, _ = fiff_open(fname)
     with f as fid:
         #   Find all forward solutions
@@ -861,9 +879,7 @@ def write_forward_solution(fname, fwd, overwrite=False, verbose=None):
 
     Parameters
     ----------
-    fname : path-like
-        File name to save the forward solution to. It should end with
-        ``-fwd.fif`` or ``-fwd.fif.gz``.
+    %(fname_fwd)s
     fwd : Forward
         Forward solution.
     %(overwrite)s
@@ -889,13 +905,28 @@ def write_forward_solution(fname, fwd, overwrite=False, verbose=None):
     forward solution with :func:`read_forward_solution`.
     """
     check_fname(
-        fname, "forward", ("-fwd.fif", "-fwd.fif.gz", "_fwd.fif", "_fwd.fif.gz")
+        fname,
+        "forward",
+        ("-fwd.fif", "-fwd.fif.gz", "_fwd.fif", "_fwd.fif.gz", "-fwd.h5", "_fwd.h5"),
     )
 
     # check for file existence and expand `~` if present
     fname = _check_fname(fname, overwrite)
-    with start_and_end_file(fname) as fid:
-        _write_forward_solution(fid, fwd)
+    if fname.suffix == ".h5":
+        _write_forward_hdf5(fname, fwd)
+    else:
+        with start_and_end_file(fname) as fid:
+            _write_forward_solution(fid, fwd)
+
+
+def _write_forward_hdf5(fname, fwd):
+    _, write_hdf5 = _import_h5io_funcs()
+    write_hdf5(fname, dict(fwd=fwd), overwrite=True)
+
+
+def _read_forward_hdf5(fname):
+    read_hdf5, _ = _import_h5io_funcs()
+    return Forward(read_hdf5(fname)["fwd"])
 
 
 def _write_forward_solution(fid, fwd):

mne/forward/tests/test_forward.py

@@ -197,6 +197,15 @@ def test_io_forward(tmp_path):
     fwd_read = read_forward_solution(fname_temp)
     assert_forward_allclose(fwd, fwd_read)
 
+    h5py = pytest.importorskip("h5py")
+    pytest.importorskip("h5io")
+    fname_h5 = fname_temp.with_suffix(".h5")
+    fwd.save(fname_h5)
+    with h5py.File(fname_h5, "r"):
+        pass  # just checks for hdf5-ness
+    fwd_read = read_forward_solution(fname_h5)
+    assert_forward_allclose(fwd, fwd_read)
+
 
 @testing.requires_testing_data
 def test_apply_forward():

mne/utils/docs.py

@@ -1694,6 +1694,15 @@ def _reflow_param_docstring(docstring, has_first_line=True, width=75):
     Name of the output file.
 """
 
+docdict[
+    "fname_fwd"
+] = """
+fname : path-like
+    File name to save the forward solution to. It should end with
+    ``-fwd.fif`` or ``-fwd.fif.gz`` to save to FIF, or ``-fwd.h5`` to save to
+    HDF5.
+"""
+
 docdict[
     "fnirs"
 ] = """