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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 choices(self):
 """Available choices for characters to be generated."""

        if self._choices:
            return self._choices
        for n in os.listdir(self._voicedir):
            if len(n) == 1 and os.path.isdir(os.path.join(self._voicedir, n)):
                self._choices.append(n)
        return self._choices