uploader.py fails on protocol-relative URL

[nemobis]

#########################################################################
# Uploading http://imslp.org/api.php
#########################################################################
imslporg-20200209-wikidump.7z found
imslporg-20200209-history.xml.7z found
imslporg-20200209-wikidump.7z was not uploaded before
http://imslp.org/api.php imslporg 20200209 imslporg-20200209-wikidump.7z
Traceback (most recent call last):
  File "uploader.py", line 301, in <module>
    main()
  File "uploader.py", line 298, in main
    upload(wikis, config, uploadeddumps)
  File "uploader.py", line 169, in upload
    r = requests.get(url=baseurl, headers=headers)
  File "/home/users/federico/.local/lib/python2.7/site-packages/requests/api.py", line 75, in get
    return request('get', url, params=params, **kwargs)
  File "/home/users/federico/.local/lib/python2.7/site-packages/requests/api.py", line 60, in request
    return session.request(method=method, url=url, **kwargs)
  File "/home/users/federico/.local/lib/python2.7/site-packages/requests/sessions.py", line 519, in request
    prep = self.prepare_request(req)
  File "/home/users/federico/.local/lib/python2.7/site-packages/requests/sessions.py", line 462, in prepare_request
    hooks=merge_hooks(request.hooks, self.hooks),
  File "/home/users/federico/.local/lib/python2.7/site-packages/requests/models.py", line 313, in prepare
    self.prepare_url(url, params)
  File "/home/users/federico/.local/lib/python2.7/site-packages/requests/models.py", line 387, in prepare_url
    raise MissingSchema(error)
requests.exceptions.MissingSchema: Invalid URL '//imslp.org/wiki/Main_Page': No schema supplied. Perhaps you meant http:////imslp.org/wiki/Main_Page?