code: def namespace_from_uri(uri):
      
      patterns = ['http://www.openbel.org/bel/[pragm]_([A-Za-z]+)_.*',
                  'http://www.openbel.org/bel/[a-z]+_[pr]_([A-Za-z]+)_.*',
                  'http://www.openbel.org/bel/[a-z]+_complex_([A-Za-z]+)_.*',
                  'http://www.openbel.org/bel/complex_([A-Za-z]+)_.*']
      for pr in patterns:
          match = re.match(pr, uri)
          if match is not None:
              return match.groups()[0]
      return None
docs: Return the entity namespace from the URI. Examples:
      http://www.openbel.org/bel/p_HGNC_RAF1 -> HGNC
      http://www.openbel.org/bel/p_RGD_Raf1 -> RGD
      http://www.openbel.org/bel/p_PFH_MEK1/2_Family -> PFH