split up large setup function

nominatim/clicmd/args.py

@@ -1,7 +1,12 @@
 """
 Provides custom functions over command-line arguments.
 """
+import logging
+from pathlib import Path
 
+from nominatim.errors import UsageError
+
+LOG = logging.getLogger()
 
 class NominatimArgs:
     """ Customized namespace class for the nominatim command line tool
@@ -25,3 +30,20 @@ class NominatimArgs:
                                      main_index=self.config.TABLESPACE_PLACE_INDEX
                                     )
                    )
+
+
+    def get_osm_file_list(self):
+        """ Return the --osm-file argument as a list of Paths or None
+            if no argument was given. The function also checks if the files
+            exist and raises a UsageError if one cannot be found.
+        """
+        if not self.osm_file:
+            return None
+
+        files = [Path(f) for f in self.osm_file]
+        for fname in files:
+            if not fname.is_file():
+                LOG.fatal("OSM file '%s' does not exist.", fname)
+                raise UsageError('Cannot access file.')
+
+        return files