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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_goone2ntletter(self, go2dcnt, depth2goobjs):
 """Assign letters to depth-01 GO terms ordered using descendants cnt."""

        # 1. Group level-01/depth-01 GO terms by namespace
        ns2dcntgoobj = cx.defaultdict(list)
        for goobj in depth2goobjs[1]:
            dcnt = go2dcnt[goobj.id]
            ns2dcntgoobj[goobj.namespace].append((dcnt, goobj))
        # 2. Assign letters to level-01/depth-01 GO terms
        go2nt = {}
        ntobj = cx.namedtuple("NtGoLetters", "D1 dcnt goobj")
        _go2abc = self.go2letter
        letters = list(chain(range(ord('A'), ord('Z') + 1), range(ord('a'), ord('z') + 1)))
        for list_dcnt_goobj in ns2dcntgoobj.values():
            letter_idx = 0
            for dcnt, goobj in sorted(list_dcnt_goobj, key=lambda t: t[0], reverse=True):
                letter = chr(letters[letter_idx]) if _go2abc is None else _go2abc.get(goobj.id, '')
                go2nt[goobj.id] = ntobj._make([letter, dcnt, goobj])
                letter_idx += 1
        return go2nt