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In [263]: parse.generate_date('2012.9.16')
Out[263]: datetime.datetime(2012, 9, 16, 0, 0)

In [264]: parse.generate_date('10-3')
Out[264]: datetime.datetime(2012, 10, 3, 0, 0)

In [265]: parse.generate_date('30')
Out[265]: datetime.datetime(2012, 8, 30, 0, 0)

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import re
import datetime

FORMAT = 'ymd'
CHANGE_SHORT_YEAR = True

def generate_date(date_args, formatstring=None):
    '''generate_date(date_args[, formatdate_args]) -> datetime-object
    
    Extract potential date digits from 'date_args' and return
    a valid datetime-object or raise a ValueError.

    'date_args' must be a date_args with 1, 2 or 3 digit(s) seperated
    by any char. These digit(s) represents year, month and day 
    in order of the given 'formatdate_args' or by 'parse.FORMAT' 
    by default.

    If one or more digit(s) are not given it will be replaced
    with the equivalent of the current day.
    Note that 2 digits are always interpreted as day with month,
    1 digit always as day.

    'formatdate_args' specified the order in which the date digits
    are contained in 'date_args'.

    If 'parse.CHANGE_SHORT_YEAR' is True, a year-number larger
    then 100 will be interpreted as a 21 century year, e. g. 
    the year 13 will be returned as year 2013.'''

    if formatstring is None:
        formatstring = FORMAT
    date_args = re.findall('\d+', date_args)
    arg_count = len(date_args)
    year, month, day = datetime.datetime.now().timetuple()[0:3]
    if arg_count == 3:
        # positions of year, month, date
        y_idx, m_idx, d_idx = formatcode_positions(formatstring, 'ymd')
        year = int(date_args[y_idx])
        if CHANGE_SHORT_YEAR and year < 100:
            year += 2000
        month = int(date_args[m_idx])
        day = int(date_args[d_idx])
    elif arg_count == 2:
        # positions of month and date if no year is given
        m_idx, d_idx = formatcode_positions(formatstring, 'md')
        month = int(date_args[m_idx])
        day = int(date_args[d_idx])
    else:
        day = int(date_args[0])
    try:
        return datetime.datetime(year, month, day)
    except ValueError:
        raise ValueError('{0}(y), {1}(m), {2}(d) seems not to be '
                         'a valid date.'.format(year, month, day))
        

def formatcode_positions(formatstring, formatcodes):
    formatcodes = formatcodes.upper()
    _ = [f.upper() for f in re.findall('[{0}]'.format(formatcodes),
                                       formatstring, re.I)]
    return [_.index(code) for code in formatcodes]

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_, x, _ = 1, 2, 3

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    ...
    if arg_count == 3:
        # positions of year, month, date
        ...
    elif arg_count == 2:
        # positions of month and date if no year is given
        ...
    else:
        ...

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date_format = 'ymd'
date_proposal = (2012, 8, 29)
date_args = (9, 16)
fill_with_defaults(date_proposal, date_args, 2012)

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        ...
    elif len_li == 8:
        ...
    elif len_li in (12, 14):
        ...