write_accessor returns filename, not path

model_server/base/session.py

@@ -148,11 +148,16 @@ class _Session(object):
     def write_accessor(self, acc_id: str, filename: Union[str, None] = None) -> str:
         """
         Write an accessor to file and unload it from the session
+        :param acc_id: accessor's ID
+        :param filename: force use of a specific filename, raise InvalidPathError if this already exists
+        :return: name of file
         """
         if filename is None:
             fp = self.paths['outbound_images'] / f'{acc_id}.tif'
         else:
             fp = self.paths['outbound_images'] / filename
+            if fp.exists():
+                raise InvalidPathError(f'Cannot overwrite file {filename} when writing accessor')
         acc = self.get_accessor(acc_id, pop=True)
 
         old_fp = self.accessors[acc_id]['filepath']
@@ -163,7 +168,7 @@ class _Session(object):
 
         acc.write(fp)
         self.accessors[acc_id]['filepath'] = fp.__str__()
-        return fp.__str__()
+        return fp.name
 
     @staticmethod
     def make_paths(root: str = None) -> dict: