connect two mathod to the same button in pyq5

1self.trainPreproBtn.clicked.connect(self.connectionFunction)
2
3@pyqtSlot()
4def connectionFunction(self):
5    self.firstFunction()
6    self.secondFunction()

1self.trainPreproBtn.clicked.connect(self.preproClicked, self.thresClicked)
2
3@pyqtSlot()
4def preproClicked(self):
5    gray = cv2.cvtColor(self.image, cv2.IMREAD_COLOR)
6    self.image = cv2.cvtColor(gray,cv2.COLOR_BGR2GRAY)
7    #(thresh, im_bw) = cv2.threshold(self.image, 128, 255, cv2.THRESH_BINARY | cv2.THRESH_OTSU)
8    #resize_image = cv2.resize(im_bw, (180, 180))
9    self.displayImage(2)
10@pyqtSlot()
11def thresClicked(self):
12    gray = cv2.cvtColor(self.image, cv2.IMREAD_COLOR)
13    self.image = cv2.cvtColor(gray, cv2.COLOR_BGR2GRAY)
14    self.image = cv2.threshold(self.image, 128, 255, cv2.THRESH_BINARY )
15    self.displayImage(4)