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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 get_report_raw(year, report_type):
 """Download and extract a CO-TRACER report. Generate a URL for the given report, download the corresponding archive, extract the CSV report, and interpret it using the standard CSV library. @param year: The year for which data should be downloaded. @type year: int @param report_type: The type of report that should be downloaded. Should be one of the strings in constants.REPORT_TYPES. @type report_type: str @return: A DictReader with the loaded data. Note that this data has not been interpreted so data fields like floating point values, dates, and boolean values are still strings. @rtype: csv.DictReader """

    if not is_valid_report_type(report_type):
        msg = '%s is not a valid report type.' % report_type
        raise ValueError(msg)

    url = get_url(year, report_type)
    raw_contents = get_zipped_file(url)
    return csv.DictReader(cStringIO.StringIO(raw_contents))