Parsing GML from owslib fails with UnboundLocalError

从 traceback 中确定的入口点 pygml.parse 开始，使用提供的 OWSLib WFS 响应和 GML 内容重现该故障。跟踪此 FeatureCollection 及其 gml:MultiSurface 几何图形的处理方式；完成标准是示例能够在没有 UnboundLocalError 的情况下完成解析，并且该行为由适当的回归检查覆盖。

I'm trying to parse a Geography Markup Language (GML) string as returned by owslib when querying a Web Feature Service (WFS). Unfortunately, this fails with UnboundLocalError.

Example:

from owslib.wfs import WebFeatureService
import pygml
wfs11 = WebFeatureService(url='http://geoserv.weichand.de:8080/geoserver/wfs', version='1.1.0')
response = wfs11.getfeature(typename='bvv:gmd_ex', bbox=(4500000,5500000,4500500,5500500), srsname='urn:x-ogc:def:crs:EPSG:31468')
content = response.read()
geom = pygml.parse(content)

Result:

Traceback (most recent call last):
  File "/data/gholl/checkouts/protocode/mwe/pygml-unboundlocalerror.py", line 6, in <module>
    geom = pygml.parse(content)
  File "/data/gholl/mambaforge/envs/py310/lib/python3.10/site-packages/pygml/parse.py", line 58, in parse
    return Geometry(result)
UnboundLocalError: local variable 'result' referenced before assignment

The first 2000 characters of content are:

b'<?xml version="1.0" encoding="UTF-8"?><wfs:FeatureCollection xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:bvv="http://www.geodaten.bayern.de" xmlns:wfs="http://www.opengis.net/wfs" xmlns:gml="http://www.opengis.net/gml" xmlns:ogc="http://www.opengis.net/ogc" xmlns:ows="http://www.opengis.net/ows" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" numberOfFeatures="4" timeStamp="2022-07-22T10:52:20.920Z" xsi:schemaLocation="http://www.opengis.net/wfs http://schemas.opengis.net/wfs/1.1.0/wfs.xsd http://www.geodaten.bayern.de http://geoserv.weichand.de:8080/geoserver/wfs?service=WFS&amp;version=1.1.0&amp;request=DescribeFeatureType&amp;typeName=bvv%3Agmd_ex"><gml:featureMembers><bvv:gmd_ex gml:id="gmd_ex.795"><bvv:land>BY</bvv:land><bvv:modellart>Basis-DLM#DTK25</bvv:modellart><bvv:objart>75003</bvv:objart><bvv:objart_txt>AX_KommunalesGebiet</bvv:objart_txt><bvv:objid>DEBYBDLMjK0001BW</bvv:objid><bvv:hdu_x>0</bvv:hdu_x><bvv:beginn>2016-05-24T20:29:37Z</bvv:beginn><bvv:adm>6003</bvv:adm><bvv:bez_gem>Weiden i.d.OPf.</bvv:bez_gem><bvv:bez_krs>Weiden i.d.OPf.</bvv:bez_krs><bvv:bez_lan>Freistaat Bayern</bvv:bez_lan><bvv:bez_rbz>Oberpfalz</bvv:bez_rbz><bvv:sch>09363000</bvv:sch><bvv:geom><gml:MultiSurface srsName="urn:x-ogc:def:crs:EPSG:31468" srsDimension="2"><gml:surfaceMember><gml:Polygon><gml:exterior><gml:LinearRing><gml:posList>5503715.86999956 4518551.38 5503731.78999956 4518559.73 5503708.02999956 4518562.46 5503684.51999956 4518566.97 5503668.41999956 4518571.48 5503656.81999956 4518577.92 5503631.05999956 4518589.84 5503596.90999956 4518604.01 5503574.04999956 4518612.39 5503532.67999956 4518628.61 5503499.89999956 4518642.95 5503476.89999956 4518658.89 5503452.56999956 4518679.061 5503434.37899956 4518700.005 5503422.69599956 4518706.57 5503420.66999956 4518707.143 5503407.34399956 4518710.915 5503396.02899956 4518711.76 5503355.57999956 4518706.38 5503322.18999956 4518702.9 5503309.20999956 4518702.23 5503287.339'

The last 500 are:

b'4503293.03 5503289.13999956 4503279.32</gml:posList></gml:LinearRing></gml:exterior></gml:Polygon></gml:surfaceMember><gml:surfaceMember><gml:Polygon><gml:exterior><gml:LinearRing><gml:posList>5505832.00999956 4503039.55 5505870.15999956 4503060.21 5505852.12999956 4503089.39 5505819.14999956 4503065.62 5505832.00999956 4503039.55</gml:posList></gml:LinearRing></gml:exterior></gml:Polygon></gml:surfaceMember></gml:MultiSurface></bvv:geom></bvv:gmd_ex></gml:featureMembers></wfs:FeatureCollection>'