Optimal_Page_Replacement.py

frames=int(input("Please enter the number of Page frames: "))
length=int(input("Enter the length of reference String: "))
string=[]
page_frame=[]
for i in range(length):
    no=int(input("Please enter the {0} character of the reference string: ".format(i+1,{0})))
    string.append(no)

print("The entered reference string is ",string)

#initailizing none values for page frames 
for i in range(frames):
    page_frame.append(None)

print("\nHere, None refers that the page frame in empty")
count=0
page_hit=0
continue_outer_loop=False
for i in string:
    for j in page_frame:
        if j==i:
            page_hit=page_hit+1
            count=count+1
            continue_outer_loop=True
            
    #continue if element already in page frame        
    if continue_outer_loop:
        continue_outer_loop=False
        print(i," already in memory no fault for this reference")
        continue
    else:
        #replacing intial none or empty frames    
        if None in page_frame:
            for k in page_frame:
                if k==None:
                    page_frame[page_frame.index(k)]=i
                    break
        else:
            #find out the element that will not be used recently than any other element in page frame
            index_li=[]
            element_li=[]
            for t in page_frame:
                
                for o in range(count,len(string)):
                    
                    if t==string[o]:
                        
                        index_li.append(o)
                        element_li.append(string[o])
                        break
                else:
                    #Use -1 index to denote the element which is not in the string
                    index_li.append(-1)
                    element_li.append(t)
            #find maximum or if -1 directly replace the element in page frame
            if -1 not in index_li:
                index_max=max(index_li)
                element=string[index_max]
            else:
                index_max=-1
                for p in range(len(index_li)):
                    if index_li[p]==index_max:
                        element=element_li[p]
                        break
                        
                
            #replace it with the new element
            page_frame[page_frame.index(element)]=i


            
            
    print("Page Frame: ",page_frame,"  for reference: ",i )
    count=count+1

#calculate page faults
page_fault=len(string)-page_hit
print("Page fault : ",page_fault)