def METHOD_NAME(name, sep='_', _xform_cache=_xform_cache):
    """Convert camel case to a "pythonic" name.
    If the name contains the ``sep`` character, then it is
    returned unchanged.
    """
    if sep in name:
        # If the sep is in the name, assume that it's already
        # transformed and return the string unchanged.
        return name
    key = (name, sep)
    if key not in _xform_cache:
        if _special_case_transform.search(name) is not None:
            is_special = _special_case_transform.search(name)
            matched = is_special.group()
            # Replace something like ARNs, ACLs with _arns, _acls.
            name = f"{name[: -len(matched)]}{sep}{matched.lower()}"
        s1 = _first_cap_regex.sub(r'\1' + sep + r'\2', name)
        transformed = _end_cap_regex.sub(r'\1' + sep + r'\2', s1).lower()
        _xform_cache[key] = transformed
    return _xform_cache[key]