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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 start_index(self, value):
 """Validate and set the vector start index."""

        # TODO: Validate contents?  (May want to set before adding the data.)
        if not isinstance(value, dict):
            raise TypeError('start_index attribute must be a dict.')
        self._start_index = value