[RDFWriter] Handle Unsupported RDF Format

Catch unsupported RDF Formats and Raise ValueError.

Related to issue #215.

Author: fschrader1992

odml/tools/format_converter.py

@@ -119,6 +119,9 @@ def _convert_file(cls, input_path, output_path, res_format):
                 p, _ = os.path.splitext(output_path)
                 output_path = p + cls._conversion_formats[res_format]
             RDFWriter(odml.load(input_path)).write_file(output_path, res_format)
+        else:
+            raise ValueError("Format for output files is incorrect. "
+                             "Please choose from the list: {}".format(cls._conversion_formats.keys()))
 
     @staticmethod
     def _create_sub_directory(dir_path):

odml/tools/rdf_converter.py

@@ -204,6 +204,9 @@ def get_rdf_str(self, rdf_format="turtle"):
                Full lists see in odml.tools.format_converter.FormatConverter._conversion_formats
         :return: string object
         """
+        if rdf_format not in self._conversion_formats:
+            raise ValueError("odml.RDFWriter.get_rdf_str: Format for output files is incorrect. "
+                             "Please choose from the list: {}".format(self._conversion_formats.keys()))
         return self.convert_to_rdf().serialize(format=rdf_format).decode("utf-8")
 
     def write_file(self, filename, rdf_format="turtle"):