def test_extractField(self, flattenFirst=lambda x: x):
        class ObjectWithRepr(object):
            def __repr__(self):
                return "repr"

        class Something(object):
            def __init__(self):
                self.number = 7
                self.object = ObjectWithRepr()

            def __getstate__(self):
                raise NotImplementedError("Just in case.")

        event = dict(
            log_format="{something.number} {something.object}",
            something=Something(),
        )

        flattened = flattenFirst(event)

        def extract(field):
            return extractField(field, flattened)

        self.assertEqual(extract("something.number"), 7)
        self.assertEqual(extract("something.number!s"), "7")
        self.assertEqual(extract("something.object!s"), "repr")
L{extractField} will extract a field used in the format string.
dataset/ETHPy150Open twisted/twisted/twisted/logger/test/test_flatten.py/FlatFormattingTests.test_extractField