Tried to execute your script today. It seems that yr.no site removed the version 1.8 of the api. The latest one is version 1.9. I have change the api version to latest one and tested again. But it still resulted in following error:-
$ python meteogram_auto.py
Traceback (most recent call last):
File "meteogram_auto.py", line 288, in <module>
fig = plot_meteogram('Oldenburg, Germany')
File "meteogram_auto.py", line 246, in plot_meteogram
latLng = retrieve_position_openmapquest(address)
File "meteogram_auto.py", line 78, in retrieve_position_openmapquest
request = urlopen(complete_url)
File "/usr/lib/python3.5/urllib/request.py", line 162, in urlopen
return opener.open(url, data, timeout)
File "/usr/lib/python3.5/urllib/request.py", line 471, in open
response = meth(req, response)
File "/usr/lib/python3.5/urllib/request.py", line 581, in http_response
'http', request, response, code, msg, hdrs)
File "/usr/lib/python3.5/urllib/request.py", line 509, in error
return self._call_chain(*args)
File "/usr/lib/python3.5/urllib/request.py", line 443, in _call_chain
result = func(*args)
File "/usr/lib/python3.5/urllib/request.py", line 589, in http_error_default
raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 403: Forbidden