allow dataloader to use descriptors (#40627)

also fixed improper uses of str()

fixes #40383

lib/ansible/parsing/dataloader.py

@@ -148,21 +148,20 @@ class DataLoader:
         :return: Returns a byte string of the file contents
         '''
         if not file_name or not isinstance(file_name, (binary_type, text_type)):
-            raise AnsibleParserError("Invalid filename: '%s'" % str(file_name))
+            raise AnsibleParserError("Invalid filename: '%s'" % to_native(file_name))
 
         b_file_name = to_bytes(self.path_dwim(file_name))
         # This is what we really want but have to fix unittests to make it pass
         # if not os.path.exists(b_file_name) or not os.path.isfile(b_file_name):
-        if not self.path_exists(b_file_name) or not self.is_file(b_file_name):
+        if not self.path_exists(b_file_name):
             raise AnsibleFileNotFound("Unable to retrieve file contents", file_name=file_name)
 
         try:
             with open(b_file_name, 'rb') as f:
                 data = f.read()
                 return self._decrypt_if_vault_data(data, b_file_name)
-
         except (IOError, OSError) as e:
-            raise AnsibleParserError("an error occurred while trying to read the file '%s': %s" % (file_name, str(e)), orig_exc=e)
+            raise AnsibleParserError("an error occurred while trying to read the file '%s': %s" % (file_name, to_native(e)), orig_exc=e)
 
     def get_basedir(self):
         ''' returns the current basedir '''