code: def _localize_df(schema_fields, df):
      
      for field in schema_fields:
          column = str(field["name"])
          if field["mode"].upper() == "REPEATED":
              continue
  
          if field["type"].upper() == "TIMESTAMP" and df[column].dt.tz is None:
              df[column] = df[column].dt.tz_localize("UTC")
  
      return df
docs: Localize any TIMESTAMP columns to tz-aware type.
  
      In pandas versions before 0.24.0, DatetimeTZDtype cannot be used as the
      dtype in Series/DataFrame construction, so localize those columns after
      the DataFrame is constructed.