QDate

# fromString negative year?

print QDate.fromString("-0720-01-01", "yyyy-MM-dd")

# output
# PyQt4.QtCore.QDate()

# what is ISODate?

# ISO 8601 extended format: either YYYY-MM-DD for dates or YYYY-MM-DDTHH:MM:SS, YYYY-MM-DDTHH:MM:SSTZD (e.g., 1997-07-16T19:20:30+01:00) for combined dates and times.

d = QDate(1, 1, 1)
print d.toString(Qt.ISODate)
print d.toString("YYYY-MM-DD")
print d.toString("yyyy-MM-dd")

# output
# 1-01-01
# YYYY-01-DD
# 0001-01-01