def _check_steps(a, b):
    """Check that the steps of ``a`` and ``b`` are both 1.

    Parameters
    ----------
    a : range
        The first range to check.
    b : range
        The second range to check.

    Raises
    ------
    ValueError
        Raised when either step is not 1.
    """
    if a.step != 1:
        raise ValueError('a.step must be equal to 1, got: %s' % a.step)
    if b.step != 1:
        raise ValueError('b.step must be equal to 1, got: %s' % b.step)
