Use QDateTime.toMSecsSinceEpoch
:
>>> import PyQt4.QtCore
>>> d = PyQt4.QtCore.QDateTime(2014, 2, 20, 17, 10, 30)
>>> d.toMSecsSinceEpoch() / 1000
1392883830L
UPDATE
Alternative using QDateTime.toTime_t
:
>>> d = PyQt4.QtCore.QDateTime(2014, 2, 20, 17, 10, 30)
>>> d.toTime_t()
1392883830L