code: def get_data_specifier(string):
      
      match = data_specifier_re.match(string)
      if match is None:
          return (None, None)
      table = match.group('table')
      if table is not None:
          table = table.strip()
      cols = _split_cols(match.group('cols'))
      return (table, cols)
docs: Return a tuple (table, col) for some [incr tsdb()] data specifier.
      For example::
  
          item              -> ('item', None)
          item:i-input      -> ('item', ['i-input'])
          item:i-input@i-wf -> ('item', ['i-input', 'i-wf'])
          :i-input          -> (None, ['i-input'])
          (otherwise)       -> (None, None)