code: def get_url_from_entry(entry):
      
      if 'url' in entry.fields:
          return entry.fields['url']
      elif entry.type.lower() == 'docushare':
          return 'https://ls.st/' + entry.fields['handle']
      elif 'adsurl' in entry.fields:
          return entry.fields['adsurl']
      elif 'doi' in entry.fields:
          return 'https://doi.org/' + entry.fields['doi']
      else:
          raise NoEntryUrlError()
docs: Get a usable URL from a pybtex entry.
  
      Parameters
      ----------
      entry : `pybtex.database.Entry`
          A pybtex bibliography entry.
  
      Returns
      -------
      url : `str`
          Best available URL from the ``entry``.
  
      Raises
      ------
      NoEntryUrlError
          Raised when no URL can be made from the bibliography entry.
  
      Notes
      -----
      The order of priority is:
  
      1. ``url`` field
      2. ``ls.st`` URL from the handle for ``@docushare`` entries.
      3. ``adsurl``
      4. DOI