PyQt and keyEventPress

Hi there! any PyQt programmer? I need to catch the keyPressed on my widgets, but I have no clue on how to do it for a given view:

class ComprobanteDeCompra_Ui(QtGui.QWidget):
    def __init__(self):
        QtGui.QWidget.__init__(self)
        self.ui = uic.loadUi("ui_ComprobanteDeCompra.ui")

How do I overwrite the KeyPressedEvent of the QLineEdit for that "ui_ComprobanteDeCompra.ui"

thanks!

^{NO EXCEPTIONS}