def retrieve(self, keyTuple):
        """Retrieves oldThing from place specified by keyTuple.

        keyTuple is a 2-tuple of coordinates."""

        # FIXME: can retrieve() share more code with insert()?
        if not self.checkKeyTuple(keyTuple):
            raise RaggedArrayException, "Bad keyTuple."
        else:
            # Key was a tuple of length 2
            # So, extract two keys.
            key1 = keyTuple[0]
            key2 = keyTuple[1]

            # So, now we have a sub-dictionary in the right position of
            # raggedArray.
            row = self.getRow(key1)
            oldThing = row.get(key2, None)
        return oldThing
Retrieves oldThing from place specified by keyTuple.

        keyTuple is a 2-tuple of coordinates.
recipes/Python/68430_Dictionarybased_twodimensional_ragged/recipe-68430.py