Implemented writing of numerical strings.

.gitignore

@@ -1,4 +1,5 @@
 __pycache__
 build
 SmallTag.egg-info
-.idea
+.idea
+tests/pytest.ini

smalltag/_formats/_id3.py

@@ -81,13 +81,17 @@ class _ID3(SmallTag, tinytag._ID3):
     def _compose_id3v2_frame(self, field_name, field_value) -> bytes:
         frame_id = bytes(self._ID3_WRITE_MAPPING[field_name], "ISO-8859-1")
 
-        field_value = field_value[0]
+        if isinstance(field_value, list):
+            field_value = field_value[0]
 
         if isinstance(field_value, str):
             frame_value = b"\x00" + bytes(field_value, "ISO-8859-1")
 
+        elif isinstance(field_value, int) and frame_id.startswith(b"T"):
+            frame_value = b"\x00" + bytes(str(field_value), "ISO-8859-1")
+
         else:
-            print(f"Writing of {field_name} is not implemented.")
+            print(f"Writing of '{field_name}' (type {type(field_value)}) is not implemented.")
             return b""
 
         frame_size = pack("4B", *self._synchsafe(len(frame_value)))

tests/formats/test_id3.py

@@ -28,3 +28,14 @@ def test_written_gets_recognized():
             assert tag.artist == field_content
             assert tag.album == field_content
 
+
+def test_int_converted_to_numerical_string():
+    tag = SmallTag.get("formats/test.mp3")
+
+    tag.track = 123
+
+    tag.write()
+
+    tag = SmallTag.get("formats/test.mp3")
+
+    assert tag.track == 123