code: def from_doi(doi):
      
      try:
          request = requests.get("http://export.arxiv.org/api/query",
                                 params={
                                     "search_query": "doi:%s" % (doi,),
                                     "max_results": 1
                                 })
          request.raise_for_status()
      except RequestException:
          return None
      root = xml.etree.ElementTree.fromstring(request.content)
      for entry in root.iter("{http://www.w3.org/2005/Atom}entry"):
          arxiv_id = entry.find("{http://www.w3.org/2005/Atom}id").text
          # arxiv_id is an arXiv full URL. We only want the id which is the last
          # URL component.
          return arxiv_id.split("/")[-1]
      return None
docs: Get the arXiv eprint id for a given DOI.
  
      .. note::
  
          Uses arXiv API. Will not return anything if arXiv is not aware of the
          associated DOI.
  
      :param doi: The DOI of the resource to look for.
      :returns: The arXiv eprint id, or ``None`` if not found.
  
      >>> from_doi('10.1209/0295-5075/111/40005')
      # Note: Test do not pass due to an arXiv API bug.
      '1506.06690'