OWSLib官方文档示例运行失败，请求排查原因

背景 #

我希望学习OWSLib或同类库，以便在Kedro数据处理管道中下载GIS数据集。按照PyPI README中的示例操作：

>>> from owslib.wms import WebMapService
>>> wms = WebMapService('http://wms.jpl.nasa.gov/wms.cgi', version='1.1.1')
>>> wms.identification.type
'OGC:WMS'
>>> wms.identification.version
'1.1.1'
>>> wms.identification.title
'JPL Global Imagery Service'
>>> wms.identification.abstract
'WMS Server maintained by JPL, worldwide satellite imagery.'

# 查看可用图层
>>> list(wms.contents)
['us_landsat_wgs84', 'modis', 'global_mosaic_base', 'huemapped_srtm',
'srtm_mag', 'daily_terra', 'us_ned', 'us_elevation', 'global_mosaic',
'daily_terra_ndvi', 'daily_aqua_ndvi', 'daily_aqua_721', 'daily_planet',
'BMNG', 'srtmplus', 'us_colordem', None, 'daily_aqua', 'worldwind_dem',
'daily_terra_721']

# 查看图层详情
>>> wms['global_mosaic'].title
'WMS Global Mosaic, pan sharpened'
>>> wms['global_mosaic'].boundingBoxWGS84
(-180.0, -60.0, 180.0, 84.0)
>>> wms['global_mosaic'].crsOptions
['EPSG:4326', 'AUTO:42003']
>>> wms['global_mosaic'].styles
{'pseudo_bright': {'title': 'Pseudo-color image (Uses IR and Visual bands,
542 mapping), gamma 1.5'}, 'pseudo': {'title': '(default) Pseudo-color
image, pan sharpened (Uses IR and Visual bands, 542 mapping), gamma 1.5'},
'visual': {'title': 'Real-color image, pan sharpened (Uses the visual
bands, 321 mapping), gamma 1.5'}, 'pseudo_low': {'title': 'Pseudo-color
image, pan sharpened (Uses IR and Visual bands, 542 mapping)'},
'visual_low': {'title': 'Real-color image, pan sharpened (Uses the visual
bands, 321 mapping)'}, 'visual_bright': {'title': 'Real-color image (Uses
the visual bands, 321 mapping), gamma 1.5'}}

# 查看可用操作与格式
>>> [op.name for op in wms.operations]
['GetTileService', 'GetCapabilities', 'GetMap']
>>> wms.getOperationByName('GetMap').methods
{'Get': {'url': 'http://wms.jpl.nasa.gov/wms.cgi?'}}
>>> wms.getOperationByName('GetMap').formatOptions
['image/jpeg', 'image/png', 'image/geotiff', 'image/tiff']

# 请求影像
>>> img = wms.getmap(   layers=['global_mosaic'],
...                     styles=['visual_bright'],
...                     srs='EPSG:4326',
...                     bbox=(-112, 36, -106, 41),
...                     size=(300, 250),
...                     format='image/jpeg',
...                     transparent=True
...                     )
>>> out = open('jpl_mosaic_visb.jpg', 'wb')
>>> out.write(img.read())
>>> out.close()

遇到的错误 #

执行代码时出现连接错误：

(vewnv) [galen@orcus Downloads]$ python
Python 3.11.3 (main, Jun  5 2023, 09:32:32) [GCC 13.1.1 20230429] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from owslib.wms import WebMapService
>>> wms = WebMapService('http://wms.jpl.nasa.gov/wms.cgi', version='1.1.1')
Traceback (most recent call last):
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/urllib3/connection.py", line 203, in _new_conn
    sock = connection.create_connection(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/urllib3/util/connection.py", line 60, in create_connection
    for res in socket.getaddrinfo(host, port, family, socket.SOCK_STREAM):
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/socket.py", line 962, in getaddrinfo
    for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
socket.gaierror: [Errno -2] Name or service not known

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/urllib3/connectionpool.py", line 790, in urlopen
    response = self._make_request(
               ^^^^^^^^^^^^^^^^^^^
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/urllib3/connectionpool.py", line 496, in _make_request
    conn.request(
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/urllib3/connection.py", line 395, in request
    self.endheaders()
  File "/usr/lib/python3.11/http/client.py", line 1278, in endheaders
    self._send_output(message_body, encode_chunked=encode_chunked)
  File "/usr/lib/python3.11/http/client.py", line 1038, in _send_output
    self.send(msg)
  File "/usr/lib/python3.11/http/client.py", line 976, in send
    self.connect()
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/urllib3/connection.py", line 243, in connect
    self.sock = self._new_conn()
                ^^^^^^^^^^^^^^^^
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/urllib3/connection.py", line 210, in _new_conn
    raise NameResolutionError(self.host, self, e) from e
urllib3.exceptions.NameResolutionError: <urllib3.connection.HTTPConnection object at 0x7f77cd407310>: Failed to resolve 'wms.jpl.nasa.gov' ([Errno -2] Name or service not known)

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/requests/adapters.py", line 486, in send
    resp = conn.urlopen(
           ^^^^^^^^^^^^^
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/urllib3/connectionpool.py", line 844, in urlopen
    retries = retries.increment(
              ^^^^^^^^^^^^^^^^^^
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/urllib3/util/retry.py", line 515, in increment
    raise MaxRetryError(_pool, url, reason) from reason  # type: ignore[arg-type]
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
urllib3.exceptions.MaxRetryError: HTTPConnectionPool(host='wms.jpl.nasa.gov', port=80): Max retries exceeded with url: /wms.cgi?service=WMS&request=GetCapabilities&version=1.1.1 (Caused by NameResolutionError("<urllib3.connection.HTTPConnection object at 0x7f77cd407310>: Failed to resolve 'wms.jpl.nasa.gov' ([Errno -2] Name or service not known)"))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/owslib/wms.py", line 50, in WebMapService
    return wms111.WebMapService_1_1_1(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/owslib/map/wms111.py", line 75, in __init__
    self._capabilities = reader.read(self.url, timeout=self.timeout)
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/owslib/map/common.py", line 65, in read
    u = openURL(spliturl[0], spliturl[1], method='Get',
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/owslib/util.py", line 209, in openURL
    req = requests.request(method.upper(), url_base, headers=headers, **rkwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/requests/api.py", line 59, in request
    return session.request(method=method, url=url, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/requests/sessions.py", line 589, in request
    resp = self.send(prep, **send_kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/requests/sessions.py", line 703, in send
    r = adapter.send(request, **kwargs)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/galen/Downloads/vewnv/lib/python3.11/site-packages/requests/adapters.py", line 519, in send
    raise ConnectionError(e, request=request)
requests.exceptions.ConnectionError: HTTPConnectionPool(host='wms.jpl.nasa.gov', port=80): Max retries exceeded with url: /wms.cgi?service=WMS&request=GetCapabilities&version=1.1.1 (Caused by NameResolutionError("<urllib3.connection.HTTPConnection object at 0x7f77cd407310>: Failed to resolve 'wms.jpl.nasa.gov' ([Errno -2] Name or service not known)"))

原因分析 #

示例无法运行的核心原因是**wms.jpl.nasa.gov域名无法解析**，说明美国喷气推进实验室（JPL）的该WMS服务已下线，或域名发生变更，导致示例中的服务地址失效，无法建立网络连接。

解决方案 #

• 替换为当前可用的公共WMS服务地址，例如：
  • OpenStreetMap的WMS服务：https://ows.terrestris.de/osm/service
  • USGS（美国地质调查局）的WMS服务
  • ESA（欧洲航天局）的相关GIS服务
• 更换地址前，先通过浏览器访问服务的GetCapabilities接口确认可用性，例如访问https://ows.terrestris.de/osm/service?service=WMS&request=GetCapabilities，能正常返回XML内容则说明服务可用
• 修改代码中的服务地址为可用URL后，重新执行后续操作

内容的提问来源于stack exchange，提问作者Galen