Python Datetime string parsing: How to know what has been parsed?

Question

I want to use Python to parse a user input string and need to know which portion of date has been specified, e.g.,

"Jan. 2017" => Month = 1, Year = 2017

The result should tell me only month and year are specified in the string, and return those values, while:

"2003-05-01"

specifies day, month and year.

I tried to use dateutil.parser.parse, and gave it a rare default date value. e.g., 1900/01/01, and then compare the parsed result with the default date and see the difference. But if the month or day are both 1 in the parsed result, it needs one more round of parsing with a different default value, in order to rule out the possibility of it being the default value, or from the user input.

The above way seems quirky. Is there a library for me to parse commonly used date string format and knowing what has been parsed?

Answer 1

I ended up doing the quirky way:

from dateutil.parser import parse
# parse the date str, and return day/month/year specified in the string.
# the value is None if the string does not have information
def parse_date(date_str):
    # choose two different dates and see if two parsed results
    default_date1 = datetime.datetime(1900, 1, 1, 0, 0)
    default_date2 = datetime.datetime(1901, 12, 12, 0, 0)
    year = None
    month = None
    day  = None
    try:
        parsed_result1 = parse(date_str, default=default_date1)
        parsed_result2 = parse(date_str, default=default_date2)
        if parsed_result1.year == parsed_result2.year: year = parsed_result2.year
        if parsed_result1.month == parsed_result2.month: month = parsed_result2.month
        if parsed_result1.day == parsed_result2.day: day = parsed_result2.day
        return year, month, day
    except ValueError:
        return None, None, None