So for my assignment, I have to show panning of a graph. But it doesnt work. Can anyone help???? Please

I used this code:

def pann_input():

        x=0
        y=0

        FASTAa=open("P04637.fas", "r")  
        header=FASTAa.readline()

        a=""    
        for ll in FASTAa:  
            #print ll
            a+=ll.rstrip()
        al=list(FASTAa)

        FASTAb=open("Q0VCX4.fas", "r") # r means read
        header=FASTAb.readline()
        b=""
        for ll in FASTAb:  
            #print ll
            b+=ll.rstrip()
        bl=list(FASTAb)

try:
        p1=str(a[x:(x+75)])
        p2=str(b[y:(y+25)])

        print " ", ' '.join(p1), " "
        for i in p2:
                print "\n" "%s" %i,
                for x in p1:
                        if i==x in p2:
                                print '*',
                        else: 
                                print ' ' , 
except IOError:
        print "Error: Give a different name:"

def limits():    
        while True:
                try:
        # Dotplot shifting
                        option = raw_input('\nEnter [r]ight, [l]eft, [u]p, [d]own or [m]enu: ')
                        if option == 'r':
                                if limits['x_right'] < limits['x_max']:
                                        limits['x_right'] += 10
                                        limits['x_left'] += 10
                        if option == 'l':
                                if limits['x_left'] > 0:
                                        limits['x_left'] -= 10
                                        limits['x_right'] -= 10
                        if option == 'u':
                                if limits['y_up'] > 0:
                                        limits['y_down'] -= 10
                                        limits['y_up'] -= 10
                        if option == 'd':
                                if limits['y_down'] < limits['y_max']:
                                        limits['y_down'] += 10
                                        limits['y_up'] += 10
                        if option == 'm':
                                print "Do you want to go to the Menu?"
                except ValueError:
                        print "Error"

pann_input()
limits()