mailbox.py 文件源码

def _search_end(self):
        self.fp.readline()      # Throw away header line
        while 1:
            pos = self.fp.tell()
            line = self.fp.readline()
            if not line:
                return
            if line[:5] == 'From ' and self._isrealfromline(line):
                self.fp.seek(pos)
                return

    # An overridable mechanism to test for From-line-ness.  You can either
    # specify a different regular expression or define a whole new
    # _isrealfromline() method.  Note that this only gets called for lines
    # starting with the 5 characters "From ".
    #
    # BAW: According to
    #http://home.netscape.com/eng/mozilla/2.0/relnotes/demo/content-length.html
    # the only portable, reliable way to find message delimiters in a BSD (i.e
    # Unix mailbox) style folder is to search for "\n\nFrom .*\n", or at the
    # beginning of the file, "^From .*\n".  While _fromlinepattern below seems
    # like a good idea, in practice, there are too many variations for more
    # strict parsing of the line to be completely accurate.
    #
    # _strict_isrealfromline() is the old version which tries to do stricter
    # parsing of the From_ line.  _portable_isrealfromline() simply returns
    # true, since it's never called if the line doesn't already start with
    # "From ".
    #
    # This algorithm, and the way it interacts with _search_start() and
    # _search_end() may not be completely correct, because it doesn't check
    # that the two characters preceding "From " are \n\n or the beginning of
    # the file.  Fixing this would require a more extensive rewrite than is
    # necessary.  For convenience, we've added a PortableUnixMailbox class
    # which does no checking of the format of the 'From' line.