MultiPolygon constructor behavior

Expected behavior and actual behavior.

The MultiPolygon constructor seems to behave oddly when provided a sequence containing other MP objects.

See behavior example on nbviewer.

Steps to reproduce the problem.

see nbviewer link

Operating system

Windows 10

Shapely version and provenance

1.6.4 from Chris Gohlke’s whl file page

[miker985]

@sgillies would you be amenable to raising an error instead of silently truncating the multipolygon instance passed to MultiPolygon to its first component polygon?

[Ricyteach]

I agree this makes the most sense.

But it does pose a problem: what is the best way to take a sequence of geometry objects, any of which could be multi or single, and combining them? Not into a union but as a “bag of” single geometries? Note that GeometryCollection doesn’t work the way that I mean:

>>> c=geo.GeometryCollection([geo.Polygon([(1,0),(2,0),(2,2),(1,2)]),geo.MultiPolygon([geo.Polygon([(0,0),(0,1),(1,1)]), geo.Polygon([(0,0),(1,0),(1,1)])])])
>>> c[0]
<shapely.geometry.polygon.Polygon object at 0x000001DB0347D940>
>>> c[1]
<shapely.geometry.multipolygon.MultiPolygon object at 0x000001DB0348C4E0>

The collection keeps the multi and single parts separate. The only way to do this I can see is:

x = []
for g in multis_and_singles:
    try:
        x.extend([*g])
    except TypeError:
        x.append(g)

mp = MultiPolygon(x)