Python validator for Library of Congress's Extended Date/Time Format (Level 1)

edtf_lvl1_validator.py

import re

def is_valid_edtf(raw_string):
    intervals = raw_string.split('/')
    if len(intervals) == 1:
        d1, = intervals
        return validate_single_date(d1)
    elif len(intervals) == 2:
        d1, d2 = intervals
        return bool(
            (d1 == 'unknown' or validate_single_date(d1)) and
            (d2 == 'unknown' or d2 == 'open' or validate_single_date(d2)) )
    else:
        return False

def validate_single_date(date_str):
    date_str = re.sub('[~?]*$', '', date_str)
    date_parts = date_str.split('-')

    unclear_year = re.compile(
        r'^-?\d{0,2}(?:\d{2}|\du|uu)$')
    known_year = re.compile(
        r'^-?(?:\d{1,4}|y\d{5,})$')
    possibly_unclear = re.compile(
        r'^(?:\d{2}|uu)$')

    tests = []

    if len(date_parts) == 1:
        year, = date_parts
        tests.append(bool(
            re.match(unclear_year, year) or re.match(known_year, year) ))

    elif len(date_parts) == 2:
        year, month = date_parts
        tests.append(bool(
            re.match(known_year, year) and re.match(possibly_unclear, month) ))
        if re.match(r'\d', month):
            tests.append( 1 <= int(m) <= 12 or 21 <= int(m) <= 24 )

    elif len(date_parts) == 3:
        year, month, day = date_parts
        tests.append(bool(re.match(known_year, year) and
            ((month == 'uu' and day == 'uu') or
            (re.match(r'^\d{2}', month) and re.match(possibly_unclear, day))) ))
        if re.match(r'\d', month):
            tests.append( 1 <= int(m) <= 12 )
        if re.match(r'\d', day):
            tests.append( 1 <= int(d) <= 31 )

    else:
        tests.append(False)

    return all(tests)