mailman_pattern.py

import re
import sys
def e(arg):
    return re.escape(arg)
def any(arg):
    return "("+"|".join(map(re.escape,arg.split()))+")"
def non_space():
    return r"\S+"
def spaced(*args):
    return "\s+".join(args)
def digits(n,n2=None):
    if n2 is None:
        return r"\d{"+str(n)+"}"
    else:
        return r"\d{"+str(n)+","+str(n2)+"}"
def lines(*arg):
    return ("^"+r"\n".join(arg)+"$")

def free():
    return(".*?")
def o(arg):
    return("("+arg+")?")
def join(*arg):
    return "".join(arg)
def nl():
    return r"\n"
def mailman_time():
    return ":".join((digits(2) for i in range(3)))
def mailman_date():
    return spaced(any("Mon Tue Wed Thu Fri Sat Sun"),
                  any("Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec"),
                  digits(0,2),
                  mailman_time(),
                  digits(4))
def mailman_mail():
    return spaced(non_space(),
                  e("at"),
                  non_space())
def mail_header(name):
    return spaced(e(name)+":",
                  free()+"$"
                  +r"(\n\t\S"+free()+"$)*"
    )
    
def mail_header_nl(name):
    return join(mail_header(name),nl())
def mailman_header():
    return join(lines(spaced(e("From"),
                             mailman_mail(),
                             mailman_date()),
                    
                      spaced(e("From:"),
                             mailman_mail(),
                             r".*?"),
                      mail_header("Date"),
                      mail_header("Subject")),
                
                nl(),
                o(mail_header_nl("In-Reply-To")),
                
                o(mail_header_nl("References")),
                o(mail_header_nl("Message-ID")),
                "^$"
    )


if __name__  == "__main__":
    header = re.compile(mailman_header(),re.MULTILINE
                        )
    print(mailman_header())
    for line in header.finditer(sys.stdin.read()):
            print(line.group())