Python's dateutil module, everybody!

gistfile1.txt

>>> from dateutil import parser

>>> parser.parse('0001-01-01')
datetime.datetime(2001, 1, 1, 0, 0)

>>> parser.parse('0010-01-01')
datetime.datetime(2001, 10, 1, 0, 0)

>>> parser.parse('0015-01-01')
datetime.datetime(2001, 1, 15, 0, 0)

>>> parser.parse('0050-01-01')
datetime.datetime(2050, 1, 1, 0, 0)

>>> parser.parse('0070-01-01')
datetime.datetime(1970, 1, 1, 0, 0)

>>> parser.parse('0080-01-01')
datetime.datetime(1980, 1, 1, 0, 0)

>>> parser.parse('0090-01-01')
datetime.datetime(1990, 1, 1, 0, 0)

>>> parser.parse('0099-01-01')
datetime.datetime(1999, 1, 1, 0, 0)

>>> parser.parse('0100-01-01')
datetime.datetime(100, 1, 1, 0, 0)

>>> parser.parse('1000-01-01')
datetime.datetime(1000, 1, 1, 0, 0)