Documentation

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.