File format to extension function

sbol3/document.py

@@ -279,6 +279,27 @@ def _guess_format(self, fpath: str):
             rdf_format = 'nt11'
         return rdf_format
 
+    @staticmethod
+    def file_extension(file_format: str) -> str:
+        """Return standard extensions when provided the document's file format
+
+        :param file_format: The format of the file
+        :return: A file extension, including the leading '.'
+        """
+        # dictionary having keys as valid file formats,
+        # and their standard extensions as value
+        types_with_standard_extension = {
+            SORTED_NTRIPLES: '.nt',
+            NTRIPLES: '.nt',
+            JSONLD: '.json',
+            RDF_XML: '.xml',
+            TURTLE: '.ttl'
+        }
+        if file_format in types_with_standard_extension:
+            return types_with_standard_extension[file_format]
+        else:
+            raise ValueError('Provided file format is not a valid one.')
+
     # Formats: 'n3', 'nt', 'turtle', 'xml'
     def read(self, location: str, file_format: str = None) -> None:
         if file_format is None:

test/test_document.py

@@ -38,6 +38,21 @@ def document_checker(thing: sbol3.Identified):
             self.assertEqual(document, thing.document)
         return document_checker
 
+    def test_file_extension(self):
+        """ Test obtaining standard extensions from file format"""
+        file_format_1 = sbol3.SORTED_NTRIPLES
+        file_format_2 = sbol3.RDF_XML
+        file_format_3 = 'Test_Format'
+        # 1. testing for sorted ntriples
+        extension_1 = sbol3.Document.file_extension(file_format_1)
+        self.assertEqual(extension_1, '.nt')
+        # 2. testing for rdf xml
+        extension_2 = sbol3.Document.file_extension(file_format_2)
+        self.assertEqual(extension_2, '.xml')
+        # 3. for invalid file formats, valueError must be raised
+        with self.assertRaises(ValueError):
+            extension_3 = sbol3.Document.file_extension(file_format_3)
+
     def test_read_ntriples(self):
         # Initial test of Document.read
         filename = 'model.nt'