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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 merge_obs(self):
 """ Match forecasts and observations. """

        for model_type in self.model_types:
            self.matched_forecasts[model_type] = {}
            for model_name in self.model_names[model_type]:
                self.matched_forecasts[model_type][model_name] = pd.merge(self.forecasts[model_type][model_name],
                                                                          self.obs, right_on="Step_ID", how="left",
                                                                          left_index=True)