def interpolate_bool(a, b, fraction):
    """Step interpolation.

    Parameters
    ----------
    a :
        initial value
    b :
        final value
    fraction : float
        fraction to interpolate to between a and b.

    Returns
    ----------
    a or b :
        Step interpolated value between a and b.
    """
    if fraction < 0.5:
        return a
    else:
        return b