The expression FileClass(file_name, field_name, config=self.config) looks wrong. It substitutes an instance of FormParserConfig for a FileConfig parameter. These bundles are conceptually different; in particular, there is no way to specify a value for UPLOAD_DELETE_TMP unless you violate the specification for FormParserConfig.
The expression
FileClass(file_name, field_name, config=self.config)looks wrong. It substitutes an instance ofFormParserConfigfor aFileConfigparameter. These bundles are conceptually different; in particular, there is no way to specify a value forUPLOAD_DELETE_TMPunless you violate the specification forFormParserConfig.