def _ensure_array_list(arrays):
    """Ensures that every element in a list is an instance of a numpy array."""
    # Note: the isinstance test is needed below so that instances of FieldArray
    # are not converted to numpy arrays
    return [numpy.array(arr, ndmin=1) if not isinstance(arr, numpy.ndarray)
            else arr for arr in arrays]
Ensures that every element in a list is an instance of a numpy array.