def check_impl(self):
        """
        Overridden to open the left and right zipfiles and to provide all
        subchecks with an open ZipFile instance rather than having
        them all open and close the ZipFile individually. For the
        duration of the check (which calls collect_impl), the
        attributes self.lzip and self.rzip will be available and used
        as the ldata and rdata of all subchecks.
        """

        with open_zip(self.ldata) as lzip:
            with open_zip(self.rdata) as rzip:
                self.lzip = lzip
                self.rzip = rzip
                ret = super(JarContentsChange, self).check_impl()

        self.lzip = None
        self.rzip = None

        return ret
Overridden to open the left and right zipfiles and to provide all
        subchecks with an open ZipFile instance rather than having
        them all open and close the ZipFile individually. For the
        duration of the check (which calls collect_impl), the
        attributes self.lzip and self.rzip will be available and used
        as the ldata and rdata of all subchecks.