<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _dict_native_ok(d):
 """ This checks if a dictionary can be saved natively as HDF5 groups. If it can't, it will be pickled. """

    if len(d) >= 256:
        return False

    # All keys must be strings
    for k in d:
        if not isinstance(k, six.string_types):
            return False

    return True