How to use the pyclipper.CT_UNION function in pyclipper

def join_polys(polys, scale=True):
    """ Given a list of polygons, merge them (union) and return a list
        of merged polygons
    """
    pc = pyclipper.Pyclipper()

    if scale:
        polys = scale_to_clipper(polys)

    results=[]
    pc.AddPaths(polys, pyclipper.PT_SUBJECT, True)
    clip_polys = pc.Execute(pyclipper.CT_UNION, pyclipper.PFT_NONZERO, 
        pyclipper.PFT_NONZERO)
    if scale:
        clip_polys = scale_from_clipper(clip_polys)
    results.extend([cp for cp in clip_polys]) 
    pc.Clear()
    return results

Before cleaning the polygon, we remove all degenerate inners. This is
    useful to remove inners which have collapsed to points or lines, which can
    interfere with the cleaning process.
    """

    # drop all degenerate inners
    clean_shape = _drop_degenerate_inners(shape)

    pc = pyclipper.Pyclipper()

    try:
        pc.AddPaths(_coords(clean_shape), pyclipper.PT_SUBJECT, True)

        # note: Execute2 returns the polygon tree, not the list of paths
        result = pc.Execute2(pyclipper.CT_UNION, pyclipper.PFT_EVENODD)

    except pyclipper.ClipperException:
        return MultiPolygon([])

    return _polytree_to_shapely(result)

x1, y1 = box1[0]
        x2, y2 = box1[1]
        box1 = np.array([[x1, y1], [x2, y1], [x2, y2], [x1, y2]])
    if len(box2) == 2:
        x1, y1 = box2[0]
        x2, y2 = box2[1]
        box2 = np.array([[x1, y1], [x2, y1], [x2, y2], [x1, y2]])
    if any(cv2.contourArea(np.int32(box)[:, np.newaxis, :]) == 0 for box in [box1, box2]):
        warnings.warn('A box with zero area was detected.')
        return 0
    pc = pyclipper.Pyclipper()
    pc.AddPath(np.int32(box1), pyclipper.PT_SUBJECT, closed=True)
    pc.AddPath(np.int32(box2), pyclipper.PT_CLIP, closed=True)
    intersection_solutions = pc.Execute(pyclipper.CT_INTERSECTION, pyclipper.PFT_EVENODD,
                                        pyclipper.PFT_EVENODD)
    union_solutions = pc.Execute(pyclipper.CT_UNION, pyclipper.PFT_EVENODD, pyclipper.PFT_EVENODD)
    union = sum(cv2.contourArea(np.int32(points)[:, np.newaxis, :]) for points in union_solutions)
    intersection = sum(
        cv2.contourArea(np.int32(points)[:, np.newaxis, :]) for points in intersection_solutions)
    return intersection / union

return paths2
    if not paths2:
        return paths1
    pc = pyclipper.Pyclipper()
    if paths1:
        if paths1[0][0] in (int, float):
            raise pyclipper.ClipperException()
        paths1 = pyclipper.scale_to_clipper(paths1, SCALING_FACTOR)
        pc.AddPaths(paths1, pyclipper.PT_SUBJECT, True)
    if paths2:
        if paths2[0][0] in (int, float):
            raise pyclipper.ClipperException()
        paths2 = pyclipper.scale_to_clipper(paths2, SCALING_FACTOR)
        pc.AddPaths(paths2, pyclipper.PT_CLIP, True)
    try:
        outpaths = pc.Execute(pyclipper.CT_UNION, pyclipper.PFT_EVENODD, pyclipper.PFT_EVENODD)
    except:
        print("paths1={}".format(paths1))
        print("paths2={}".format(paths2))
    outpaths = pyclipper.scale_from_clipper(outpaths, SCALING_FACTOR)
    return outpaths

InvalidSubjectContourError, InvalidClippingContourError, ExecutionError)
import pyclipper


"""
General Suggestions:
- Contours should only be sent here if they actually overlap.
  This can be checked easily using contour bounds.
- Only perform operations on closed contours.
- contours must have an on curve point
- some kind of a log
"""


_operationMap = {
    "union": pyclipper.CT_UNION,
    "intersection": pyclipper.CT_INTERSECTION,
    "difference": pyclipper.CT_DIFFERENCE,
    "xor": pyclipper.CT_XOR,
}

_fillTypeMap = {
    "evenOdd": pyclipper.PFT_EVENODD,
    "nonZero": pyclipper.PFT_NONZERO,
    # we keep the misspelling for compatibility with earlier versions
    "noneZero": pyclipper.PFT_NONZERO,
}


def clipExecute(subjectContours, clipContours, operation, subjectFillType="nonZero",
                clipFillType="nonZero"):
    pc = pyclipper.Pyclipper()

def union(self, poly):
        # type: (Polygon) -> List[Polygon]
        """Union with another polygon.

        :param poly: The clip polygon.
        :returns: A list of Polygons.

        """
        clipper = self._prepare_clipper(poly)
        if not clipper:
            return []
        unions = clipper.Execute(
            pc.CT_UNION, pc.PFT_NONZERO, pc.PFT_NONZERO)

        return self._process(unions)