self.centralwidget.connect(self.listWidget.item(i), QtCore.SIGNAL("clicked()"), self.test)

import sys
from PyQt4.QtGui import *
from PyQt4.QtCore import *

class MyWidget(QWidget):
    doubleClicked = pyqtSignal()
    def mouseDoubleClickEvent(self, event):
        self.doubleClicked.emit()

def iAmSlot():
    print "hello"

if __name__ == "__main__":
    app = QApplication(sys.argv)
    window = MyWidget()
    window.show()
    window.doubleClicked.connect(iAmSlot)
    sys.exit(app.exec_())