Numeric categorical values can not be written to disk

[PGijsbers]

If a categorical attribute has only numeric values (which is valid, if not somewhat unspecified, in the original arff definition), the package raises an error when writing the data to disk:

import arff
data = dict(
  relation='dataset name',
  description='dataset description',
  attributes=[("categorical_with_numeric_values", [1, 2, 3])],
  data=[[1], [2], [3]]
)
with open("test.arff", "w") as fh:
  arff.dump(data, fh)

Expected behavior: Produce a valid arff file with attribute:

@ATTRIBUTE categorical_with_numeric_values {1, 2, 3}.

Actual behavior: Treats the categories as strings, leading to an error:

Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
  File "/Users/pietergijsbers/repositories/automlbenchmark/venv/lib/python3.9/site-packages/arff.py", line 1091, in dump
    for row in generator:
  File "/Users/pietergijsbers/repositories/automlbenchmark/venv/lib/python3.9/site-packages/arff.py", line 1028, in iter_encode
    yield self._encode_attribute(attr[0], attr[1])
  File "/Users/pietergijsbers/repositories/automlbenchmark/venv/lib/python3.9/site-packages/arff.py", line 964, in _encode_attribute
    type_tmp = [u'%s' % encode_string(type_k) for type_k in type_]
  File "/Users/pietergijsbers/repositories/automlbenchmark/venv/lib/python3.9/site-packages/arff.py", line 964, in <listcomp>
    type_tmp = [u'%s' % encode_string(type_k) for type_k in type_]
  File "/Users/pietergijsbers/repositories/automlbenchmark/venv/lib/python3.9/site-packages/arff.py", line 420, in encode_string
    if _RE_QUOTE_CHARS.search(s):
TypeError: expected string or bytes-like object

Possible workaround by stringifying the categories (they are unquoted in the resulting arff header):

-  attributes=[("categorical_with_numeric_values", [1, 2, 3])],
+  attributes=[("categorical_with_numeric_values", ['1', '2,' '3'])],

Python 3.11.3, liac-arff 2.5.0

I understand there is currently no work being done on the package, but I figured I would document the bug and workaround.