code: def cat(expr, others=None, sep=None, na_rep=None):
      
  
      if others is not None:
          from .strings import _cat as cat_str
  
          return cat_str(expr, others, sep=sep, na_rep=na_rep)
  
      return _cat(expr, sep=sep, na_rep=na_rep)
docs: Concatenate strings in sequence with given separator
  
      :param expr:
      :param others: other sequences
      :param sep: string or None, default None
      :param na_rep: string or None default None, if None, NA in the sequence are ignored
      :return: