ENH: clearer error messages in copyfile_brainvision (#1444)

Author: sappelhoff

doc/whats_new.rst

@@ -52,6 +52,6 @@ Detailed list of changes
 ⚕️ Code health
 ^^^^^^^^^^^^^^
 
-- None yet
+- Made :func:`mne_bids.copyfiles.copyfile_brainvision` output more meaningful error messages when encountering problematic files, by `Stefan Appelhoff`_ (:gh:`1444`)
 
 :doc:`Find out what was new in previous releases <whats_new_previous_releases>`

mne_bids/copyfiles.py

@@ -108,17 +108,24 @@ def _get_brainvision_paths(vhdr_path):
         vmrk_file = vmrk_file_match.groups()[0]
 
     # Make sure we are dealing with file names as is customary, not paths
-    # Paths are problematic when copying the files to another system. Instead,
-    # always use the file name and keep the file triplet in the same directory
-    assert os.sep not in eeg_file
-    assert os.sep not in vmrk_file
+    for fi in [eeg_file, vmrk_file]:
+        if os.sep in fi:
+            raise RuntimeError(
+                f"Detected a path separator in a file link: {fi}.\n\n"
+                "Paths are problematic when copying the files to another system. "
+                "Instead, always use the file name and keep the "
+                "BrainVision file triplet (eeg/dat, vhdr, vmrk) in the same directory."
+            )
 
     # Assert the paths exist
     head, tail = op.split(vhdr_path)
     eeg_file_path = op.join(head, eeg_file)
     vmrk_file_path = op.join(head, vmrk_file)
-    assert op.exists(eeg_file_path)
-    assert op.exists(vmrk_file_path)
+    for fpath in [eeg_file_path, vmrk_file_path]:
+        if not Path(fpath).exists():
+            raise FileNotFoundError(
+                f"{fpath} referenced in {vhdr_path} but it does not exist."
+            )
 
     # Return the paths
     return (eeg_file_path, vmrk_file_path)
@@ -355,14 +362,24 @@ def copyfile_brainvision(vhdr_src, vhdr_dest, anonymize=None, verbose=None):
     # Write new header and marker files, fixing the file pointer links
     # For that, we need to replace an old "basename" with a new one
     # assuming that all .eeg/.dat, .vhdr, .vmrk share one basename
-    __, basename_src = op.split(fname_src)
-    assert op.split(eeg_file_path)[-1] in [basename_src + ".eeg", basename_src + ".dat"]
-    assert basename_src + ".vmrk" == op.split(vmrk_file_path)[-1]
-    __, basename_dest = op.split(fname_dest)
+    basename_src = Path(fname_src).name
+    eeg_expected = [f"{basename_src}.eeg", f"{basename_src}.dat"]
+    vmrk_expected = [f"{basename_src}.vmrk"]
+    if Path(eeg_file_path).name not in eeg_expected:
+        raise RuntimeError(
+            f"Unexpected path to data file in {vhdr_src}:\n    "
+            f"-->{Path(eeg_file_path).name}\nExpected one of {eeg_expected}."
+        )
+    if Path(vmrk_file_path).name not in vmrk_expected:
+        raise RuntimeError(
+            f"Unexpected path to marker file in {vhdr_src}:\n    "
+            f"-->{Path(vmrk_file_path).name}\nExpected one of {vmrk_expected}."
+        )
+    basename_dest = Path(fname_dest).name
     search_lines = [
-        "DataFile=" + basename_src + ".eeg",
-        "DataFile=" + basename_src + ".dat",
-        "MarkerFile=" + basename_src + ".vmrk",
+        f"DataFile={basename_src}.eeg",
+        f"DataFile={basename_src}.dat",
+        f"MarkerFile={basename_src}.vmrk",
     ]
 
     with open(vhdr_src, encoding=enc) as fin: