ansible/docs/docsite/rst/dev_guide/testing/sanity/no-basestring.rst

Sanity Tests » no-basestring
============================

Do not use ``isinstance(s, basestring)`` as basestring has been removed in
Python3.  You can import ``string_types``, ``binary_type``, or ``text_type``
from ``ansible.module_utils.six`` and then use ``isinstance(s, string_types)``
or ``isinstance(s, (binary_type, text_type))`` instead.

If this is part of code to convert a string to a particular type,
``ansible.module_utils._text`` contains several functions that may be even
better for you: ``to_text``, ``to_bytes``, and ``to_native``.