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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_month(datestring):
 """Transforms a written month into corresponding month number. E.g. November -> 11, or May -> 05. Keyword arguments: datestring -- a string Returns: String, or None if the transformation fails """

    convert_written = re.compile(r"jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec", re.IGNORECASE)
    month = convert_written.search(datestring)
    month_number = None

    # If there's a match, convert the month to its corresponding number
    if month:
        month_number = strptime(month.group(), "%b").tm_mon
        if month_number < 10:
            month_number = add_zero(month_number)

    return str(month_number)