def assertNoHeader(self, key, msg=None):
        """Fail if key in self.headers."""
        lowkey = key.lower()
        matches = [k for k, v in self.headers if k.lower() == lowkey]
        if matches:
            if msg is None:
                msg = `key` % '%s in headers'
            self._handlewebError(msg)
dataset/ETHPy150Open wesabe/fixofx/3rdparty/wsgi_intercept/webtest_intercept/webtest.py/WebCase.assertNoHeader/swapped operands of `%`