Unable to download JSON metadata error when trying to download periscope video with description beginning with #

[ditpara]

• I've verified and I assure that I'm running youtube-dl 2018.02.08

• At least skimmed through the README, most notably the FAQ and BUGS sections

• Searched the bugtracker for similar issues including closed ones

• Checked that provided video/audio/playlist URLs (if any) are alive and playable in a browser

• Bug report (encountered problems with youtube-dl)

youtube-dl -f mp4 -v https://www.periscope.tv/aesthetics_jb/1BdGYPXrrrBKX
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'-f', u'mp4', u'-v', u'https://www.periscope.tv/aesthetics_jb/1BdGYPXrrrBKX']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2018.02.08
[debug] Python version 2.7.10 (CPython) - Darwin-17.4.0-x86_64-i386-64bit
[debug] exe versions: ffmpeg 3.4.1, ffprobe 3.4.1
[debug] Proxy map: {}
[periscope] 1BdGYPXrrrBKX: Downloading JSON metadata
[periscope] 1BdGYPXrrrBKX: Downloading JSON metadata
ERROR: Unable to download JSON metadata: HTTP Error 404: Not Found (caused by HTTPError()); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; type  youtube-dl -U  to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
  File "/usr/local/bin/youtube-dl/youtube_dl/extractor/common.py", line 519, in _request_webpage
    return self._downloader.urlopen(url_or_request)
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 2199, in urlopen
    return self._opener.open(req, timeout=self._socket_timeout)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib2.py", line 437, in open
    response = meth(req, response)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib2.py", line 550, in http_response
    'http', request, response, code, msg, hdrs)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib2.py", line 475, in error
    return self._call_chain(*args)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib2.py", line 409, in _call_chain
    result = func(*args)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urllib2.py", line 558, in http_error_default
    raise HTTPError(req.get_full_url(), code, msg, hdrs, fp)

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• Playlist: https://www.periscope.tv/aesthetics_jb
• Single file: https://www.periscope.tv/aesthetics_jb/1BdGYPXrrrBKX
• Single file: https://www.periscope.tv/aesthetics_jb/1YpKkdjOLnAGj

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This fails both when trying to download a playlist where the first video starts with a # (or when it reaches a video that does) and on downloading single files beginning with #.

I have reported a separate bug #15554 for other characters that I found break the JSON metadata download.