code: def _extract(expr, pat, flags=0, group=0):
      
  
      return _string_op(expr, Extract, _pat=pat, _flags=flags, _group=group)
docs: Find group in each string in the Series using passed regular expression.
  
      :param expr:
      :param pat: Pattern or regular expression
      :param flags: re module, e.g. re.IGNORECASE
      :param group: if None as group 0
      :return: sequence or scalar