How to manage loops with button clicks in pyqt5

I have text file to read the values and plot a graph as a slideshow. For that I split the data into n sets for the graph to show as a slideshow. I have two list containing values as:

x_data:  [array([[-210. ],[-209.98], [-209.96],[82.54]]),array([[-82.5 ],[44.96],[44.98]]),...array([[300.  ],[300.02]])

y_data:   [array([[-10.01953],[ -1.93359],[ -5.33203],...[-10.10742]]),array([[-10.07812],[-10.07812]]),...array([[-19.6875], [-19.6875]])] . 

Six buttons are there to interrupt the slideshow graph. play ,pause, forward_multiple, backward_multiple,forward_one, backward_one

Actions required by the click of buttons are as follows:

Play button: When I click play button the graph is plotting based on the array values of x_data and y_data. (It is working)

Pause Button: Should stop currently running graph (Not working)

Forward one: Should play forward one step after the current graph.
Forward multiple: Plot graphs from the current set till the last set in the array. ie forward play from current graph till last graph.(Works, but when it reaches the last graph it exit from the app)
Backward one: Play one step backwards from the current graph playing.(Works, works for one time only. If I click again, not showing the previous graph)

Backward multiple: Play backwards from the current graph running till the starting graph.(Works, but it is looping continuously. I want to play up-to the starting graph)

class MatplotlibWidget(QMainWindow):
    def __init__(self):
        ---
        self.playbutton.clicked.connect(self.selectFile)
        self.pause_button.clicked.connect(self.stopRun)
        self.backward_btn.clicked.connect(self.backward)
        self.forward_btn.clicked.connect(self.forward)
        self.backward_multiple.clicked.connect(self.backward_multi)
        self.forward_multiple.clicked.connect(self.forward_multi)
        ---

def drawGraph(self,i):

    global  x,y,iters,val,gvalue,x_data,y_data,j,n_graphs,sec_value
    # Reading x and y values from file
    x = data[:, 0].reshape(m, 1)  
    y = data[:, col_value-1].reshape(m, 1)
    gvalue=self.graphSpinbox.value()
    iters=m //(gvalue-1)
    global current_iter
    current_iter = 0
    val=self.timeinterval_spinbox.value()
    sec_value = str(val) + str(0) + str(0) + str(0)
    x_data = []
    y_data = []
    n_graphs=[] 
    for i in range(gvalue):
        x_data.append(x[current_iter:current_iter+iters])
        y_data.append(y[current_iter:current_iter+iters])
        current_iter=current_iter+iters
    for j in range(gvalue):
        n_graphs.append(str(j + 1))           
        self.plotDraw(x_data[j],y_data[j])
        j=j+1

def plotDraw(self,x ,y):

    self.MplWidget.canvas.axes.clear()
    self.MplWidget.canvas.axes.plot(x, y)
    self.MplWidget.canvas.axes.legend(('cosinus', 'sinus'), loc='upper right')
    self.MplWidget.canvas.axes.set_title('Signal')
    self.MplWidget.canvas.draw()
    loop = QEventLoop()
    QTimer.singleShot(int(sec_value), loop.quit)
    loop.exec_()

def stopRun(self):   

    loop = QEventLoop()
    QTimer.singleShot(int(sec_value), loop.quit)
    loop.exec_()
    self.event_source.stop()

def backward(self):
    curr_pos = int(n_graphs[len(n_graphs) - 1])
    print("n_graphs: ",n_graphs)
    print("curr_pos: ",curr_pos)
    if curr_pos!=0:
        self.plotDraw(x_data[curr_pos-2], y_data[curr_pos-2])

def backward_multi(self):
    curr_pos = int(n_graphs[len(n_graphs) - 1])
    print("n_graphs: ", n_graphs)
    print("curr_pos: ", curr_pos)
    while curr_pos<=gvalue:
        self.plotDraw(x_data[curr_pos - 2], y_data[curr_pos - 2])
        curr_pos=curr_pos-1
        loop = QEventLoop()
        QTimer.singleShot(int(sec_value), loop.quit)
        loop.exec_()

def forward(self):
    print("Forward button clicked")
    print(n_graphs)
    curr_pos=int(n_graphs[len(n_graphs)-1])
    print(curr_pos)
    if curr_pos!=0:
        self.plotDraw(x_data[curr_pos],y_data[curr_pos])


def forward_multi(self):
    print(n_graphs)
    curr_pos = int(n_graphs[len(n_graphs) - 1])
    print(curr_pos)
    while curr_pos<=gvalue:
        self.plotDraw(x_data[curr_pos], y_data[curr_pos])
        curr_pos = curr_pos + 1
        loop = QEventLoop()
        QTimer.singleShot(int(sec_value), loop.quit)
        loop.exec_()