brainvisionrawio: added error message when sidecar file seems to be missing

Author: chkothe

neo/rawio/brainvisionrawio.py

@@ -55,8 +55,8 @@ def _parse_header(self):
         marker_filename = self.filename.replace(bname, vhdr_header["Common Infos"]["MarkerFile"])
         binary_filename = self.filename.replace(bname, vhdr_header["Common Infos"]["DataFile"])
 
-        binary_filename = self._ensure_filename(binary_filename, "data")
-        marker_filename = self._ensure_filename(marker_filename, "marker")
+        marker_filename = self._ensure_filename(marker_filename, "marker", "MarkerFile")
+        binary_filename = self._ensure_filename(binary_filename, "data", "DataFile")
 
         if vhdr_header["Common Infos"]["DataFormat"] != "BINARY":
             raise NeoReadWriteError(
@@ -239,7 +239,7 @@ def _rescale_event_timestamp(self, event_timestamps, dtype, event_channel_index)
     def _get_analogsignal_buffer_description(self, block_index, seg_index, buffer_id):
         return self._buffer_descriptions[block_index][seg_index][buffer_id]
 
-    def _ensure_filename(self, filename, kind):
+    def _ensure_filename(self, filename, kind, entry_name):
         if not os.path.exists(filename):
             # file not found, subsequent import stage would fail
             ext = os.path.splitext(filename)[1]
@@ -256,6 +256,29 @@ def _ensure_filename(self, filename, kind):
                     f"prefix matched the .vhdr ({os.path.basename(alt_name)}). Using "
                     f"this file instead.")
                 filename = alt_name
+            else:
+                # we neither found the file referenced in the .vhdr file nor a file of
+                # same name as header with the desired extension; most likely a file went
+                # missing or was renamed in an inconsistent fashion; generate a useful
+                # error message
+                header_dname = os.path.dirname(self.filename)
+                header_bname = os.path.basename(self.filename)
+                referenced_bname = os.path.basename(filename)
+                alt_bname = os.path.basename(alt_name)
+                if alt_bname != referenced_bname:
+                    # this is only needed when the two candidate file names differ
+                    detail = (f" is named either as per the {entry_name}={referenced_bname} "
+                              f"line in the .vhdr file, or")
+                else:
+                    # we omit it if we can to make it less confusing
+                    detail = ""
+                self.logger.error(
+                    f"Did not find the {kind} file associated with .vhdr (header) " 
+                    f"file {header_bname!r} in folder {header_dname!r}.\n  Please make "
+                    f"sure the file{detail} is named the same way as the .vhdr file, but "
+                    f"ending in {ext} (i.e. {alt_bname}).\n  The import will likely fail, "
+                    f"but if it goes through, you can ignore this message (the check "
+                    f"can misfire on networked file systems).")
         return filename