def ItemByValue(self, value):<EOL>
return self._compose_optic(optics.ItemByValueLens(value))<EOL>
A lens that focuses a single item (key-value pair) in a
        dictionary by its value. Set an item to `None` to remove it
        from the dictionary. This lens assumes that there will only be
        a single key with that particular value. If you violate that
        assumption then you're on your own.

            >>> from lenses import lens
            >>> from collections import OrderedDict
            >>> data = OrderedDict([(1, 10), (2, 20)])
            >>> lens.ItemByValue(10)
            UnboundLens(ItemByValueLens(10))
            >>> lens.ItemByValue(10).get()(data)
            (1, 10)
            >>> lens.ItemByValue(30).get()(data) is None
            True
            >>> lens.ItemByValue(10).set((3, 10))(data)
            OrderedDict([(2, 20), (3, 10)])
            >>> lens.ItemByValue(10).set(None)(data)
            OrderedDict([(2, 20)])