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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 to_observations_dataframe(self, sql_ctx, ts_col='timestamp', key_col='key', val_col='value'):
 """ Returns a DataFrame of observations, each containing a timestamp, a key, and a value. Parameters sql_ctx : SQLContext ts_col : string The name for the timestamp column. key_col : string The name for the key column. val_col : string The name for the value column. """

        ssql_ctx = sql_ctx._ssql_ctx
        jdf = self._jtsrdd.toObservationsDataFrame(ssql_ctx, ts_col, key_col, val_col)
        return DataFrame(jdf, sql_ctx)