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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 update_get_params(self):
 """Update HTTP GET params with the given fields that user wants to fetch."""

        if isinstance(self._fields, (tuple, list)):  # tuples & lists > x,y,z
            self.get_params["fields"] = ",".join([str(_) for _ in self._fields])
        elif isinstance(self._fields, str):
            self.get_params["fields"] = self._fields