Type GeometryCollection from package shapely cannot be parsed directly

[mattijn]

See following code:

from shapely import geometry

geom_collection = geometry.GeometryCollection([
    geometry.Polygon([[0, 0], [1, 0], [1, 1], [0, 1], [0, 0]]), 
    geometry.Polygon([[1, 0], [2, 0], [2, 1], [1, 1], [1, 0]])
])
geom_collection

topojson.topology(geom_collection)

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-12-2442f763691d> in <module>()
----> 1 topojson.topology(geom_collection)

~/topojson/topojson/topology.py in topology(data, snap_vertices, gridsize_to_snap, simplify, simplify_factor)
     24 
     25     # apply topology to data
---> 26     data = extractor.main(data)
     27 
     28     if snap_vertices:

~/topojson/topojson/extract.py in main(self, data)
    367 
    368         self.data = data
--> 369         self.serialize_geom_type(data)
    370 
    371         # prepare to return object

~/topojson/topojson/utils/dispatcher.py in wrapper(*args, **kw)
     16 
     17     def wrapper(*args, **kw):
---> 18         return dispatcher.dispatch(args[1].__class__)(*args, **kw)
     19 
     20     wrapper.register = dispatcher.register

~/topojson/topojson/extract.py in extract_geometrycollection(self, geom)
    177         """
    178 
--> 179         obj = self.data[self.key]
    180         self.geomcollection_counter += 1
    181         self.records_collection = len(geom)

AttributeError: 'Extract' object has no attribute 'key'

[perrette]

May I ask why the geometry collection works, but

> geom = geometry.Polygon([[0, 0], [1, 0], [1, 1], [0, 1], [0, 0]])
> topojson.Topology(geom)
...
AttributeError: 'Topology' object has no attribute 'obj'

does not?

After all, the topojson formal should also work for a single piece of geometry, shouldn't it?

[mattijn]

Sounds like a bug. Yes the topojson format should be able to support a single geometry. Never came up before as the computation of the topology cannot be done with a single geometry. I'll open a new issue to track this.