Ensure the rect spec is valid.

def check_bounding_rect(rect_pos):
    """Ensure the rect spec is valid."""

    if not isinstance(rect_pos, Iterable):
        raise ValueError('rectangle spect must be a tuple of floats '
                         'specifying (left, right, width, height)')

    left, bottom, width, height = rect_pos
    for val, name in zip((left, bottom, width, height),
                         ('left', 'bottom', 'width', 'height')):
        if val < 0.0 or val > 1.0:
            raise ValueError("{}'s value must be >=0 and <= 1.0. "
                             "It is now {}".format(name, val))

    if left + width > 1.0:
        print('rect would extend beyond the width of figure/axis by {}'.format(left + width - 1.0))

    if bottom + height > 1.0:
        print('rect would extend beyond the height of figure/axis by {}'.format(
            bottom + height - 1.0))

    return rect_pos