code: def to_url(dois):
      
      if isinstance(dois, list):
          return [DX_URL.format(doi=doi) for doi in dois]
      else:
          return DX_URL.format(doi=dois)
docs: Convert a list of canonical DOIs to a list of DOIs URLs.
  
      :param dois: List of canonical DOIs. Can also be a single canonical DOI.
      :returns: A list of DOIs URLs (resp. a single value).
  
      >>> to_url(['10.1209/0295-5075/111/40005'])
      ['http://dx.doi.org/10.1209/0295-5075/111/40005']
  
      >>> to_url('10.1209/0295-5075/111/40005')
      'http://dx.doi.org/10.1209/0295-5075/111/40005'