remove assertion for reading EDFs without preload

Author: skjerns

mne/io/edf/edf.py

@@ -436,21 +436,24 @@ def _read_segment_file(data, idx, fi, start, stop, raw_extras, filenames, cals,
                 ones[orig_idx, smp_read : smp_read + len(one_i)] = one_i
                 n_smp_read[orig_idx] += len(one_i)
 
+        # resample channels with lower sample requency
         # skip if no data was requested, ie. only annotations were read
-        if sum(n_smp_read) > 0:
+        if any(n_smp_read) > 0:
             # expected number of samples, equals maximum sfreq
             smp_exp = data.shape[-1]
-            assert max(n_smp_read) == smp_exp
 
             # resample data after loading all chunks to prevent edge artifacts
             resampled = False
+
             for i, smp_read in enumerate(n_smp_read):
                 # nothing read, nothing to resample
                 if smp_read == 0:
                     continue
                 # upsample if n_samples is lower than from highest sfreq
                 if smp_read != smp_exp:
-                    assert (ones[i, smp_read:] == 0).all()  # sanity check
+                    # sanity check that we read exactly how much we expected
+                    assert (ones[i, smp_read:] == 0).all()
+
                     ones[i, :] = resample(
                         ones[i, :smp_read].astype(np.float64),
                         smp_exp,

mne/io/edf/tests/test_edf.py

@@ -258,6 +258,27 @@ def test_edf_different_sfreqs(stim_channel):
     assert_allclose(data1, data2, err_msg="Data mismatch with preload")
     assert_allclose(times1, times2)
 
+@testing.requires_testing_data
+@pytest.mark.parametrize("stim_channel", (None, False, "auto"))
+def test_edf_different_sfreqs_nopreload(stim_channel):
+    """Test loading smaller sfreq channels without preloading"""
+
+    # load without preloading, then load a channel that has smaller sfreq
+    # as other channels, produced an error, see mne-python/issues/12897
+
+    for i in range(1, 13):
+        raw = read_raw_edf(
+            input_fname=edf_reduced,
+            verbose='error',
+            preload=False)
+
+        # this should work for channels of all sfreq, even if larger sfreqs
+        # are present in the file
+        x1 = raw.get_data(picks=[f'A{i}'], return_times=False)
+        # load next ch, this is sometimes with a higher sometimes a lower sfreq
+        x2 = raw.get_data([f'A{i+1}'], return_times=False)
+        assert x1.shape==x2.shape
+
 
 def test_edf_data_broken(tmp_path):
     """Test edf files."""