def assertHeader(self, key, value=None, msg=None):
        """Fail if (key, [value]) not in self.headers."""
        lowkey = key.lower()
        for k, v in self.headers:
            if k.lower() == lowkey:
                if value is None or str(value) == v:
                    return
        
        if msg is None:
            if value is None:
                msg = '%s not in headers' % `key`
            else:
                msg = (`key`, `value`) % '%s:%s not in headers'
        self._handlewebError(msg)
dataset/ETHPy150Open wesabe/fixofx/3rdparty/wsgi_intercept/webtest_intercept/webtest.py/WebCase.assertHeader/swapped operands of `%`