like this text = " \t hello there\n \t how are you?\n \t HHHH" hello there how are you? HHHH Could I get the common prefix substring through regex? I try to In [36]: re.findall(r"(?m)(?:(^[ \t]+).+[\n\r]+\1)", " \t hello there\n \t how are you?\n \t HHHH") Out[36]: [' \t '] But apparently that common prefix substring is ' \t ' I want use for dedent function like python textwrap module.