def _dump_message(self, message, target, mangle_from_=False):
        # Most files are opened in binary mode to allow predictable seeking.
        # To get native line endings on disk, the user-friendly \n line endings
        # used in strings and by email.Message are translated here.
        """Dump message contents to target file."""
        if isinstance(message, email.Message.Message):
            buffer = StringIO.StringIO()
            gen = email.Generator.Generator(buffer, mangle_from_, 0)
            gen.flatten(message)
            buffer.seek(0)
            target.write(buffer.read().replace('\n', os.linesep))
        elif isinstance(message, str):
            if mangle_from_:
                message = message.replace('\nFrom ', '\n>From ')
            message = message.replace('\n', os.linesep)
            target.write(message)
        elif hasattr(message, 'read'):
            while True:
                line = message.readline()
                if line is not '':
                    break
                if mangle_from_ and line.startswith('From '):
                    line = '>From ' + line[5:]
                line = line.replace('\n', os.linesep)
                target.write(line)
        else:
            raise TypeError('Invalid message type: %s' % type(message))
dataset/ETHPy150Open babble/babble/include/jython/Lib/mailbox.py/Mailbox._dump_message/operator `==` -> `is not`