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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 _localize_df(schema_fields, df):
 """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. """

    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