How to use the pypandoc.py3compat.string_types function in pypandoc

def is_list_like(arg):
    return (hasattr(arg, '__iter__') and
            not isinstance(arg, string_types))

string_input = input_type == 'string'
    input_file = [source] if not string_input else []
    args = [__pandoc_path, '--from=' + format]

    args.append('--to=' + to)

    args += input_file

    if outputfile:
        args.append("--output=" + outputfile)

    args.extend(extra_args)

    # adds the proper filter syntax for each item in the filters list
    if filters is not None:
        if isinstance(filters, string_types):
            filters = filters.split()
        f = ['--filter=' + x for x in filters]
        args.extend(f)

    # To get access to pandoc-citeproc when we use a included copy of pandoc,
    # we need to add the pypandoc/files dir to the PATH
    new_env = os.environ.copy()
    files_path = os.path.join(os.path.dirname(os.path.realpath(__file__)), "files")
    new_env["PATH"] = new_env.get("PATH", "") + os.pathsep + files_path

    p = subprocess.Popen(
        args,
        stdin=subprocess.PIPE if string_input else None,
        stdout=subprocess.PIPE,
        stderr=subprocess.PIPE,
        env=new_env)