A bad implementation of intersection via skip pointers from Chapter 2 of "Introduction to Information Retrieval"

INTERSECTWITHSKIPS.py

from math import sqrt, ceil
 
class SkipList:
    def __init__(self, list, i=0):
        self.list=list
        self.len=len(self.list)
        self.interval=ceil(sqrt(self.len))
        self.i=i
 
    def next(self):
        try:
            self.i+=1
            return self.list[self.i]
        except: pass
 
    def hasSkip(self):
        return self.i+self.interval < self.len and self.i%self.interval==0
 
    def isNotNil(self):
        return self.i<self.len
 
    def skip(self):
        return SkipList(self.list, self.i+self.interval)
 
    def doSkip(self):
        self.i+=self.interval
 
    def docID(self):
        return self.list[self.i]
 
def INTERSECTWITHSKIPS(A, B):
    intersections=[]
    A_gagal=[]
    B_gagal=[]
    A_sukses=[]
    B_sukses=[]
 
    while A.isNotNil() and B.isNotNil() :
        if A.docID() == B.docID() :
            intersections.append( A.docID() )
            if A.hasSkip():
                A_gagal.append( A.docID() )
            if B.hasSkip():
                B_gagal.append( B.docID() )
            A.next()
            B.next()
        else:
            if A.docID() < B.docID() :
                if A.hasSkip():
                    if A.skip().docID()<=B.docID() :
                        A_sukses.append( A.docID() )
                        while A.hasSkip() and A.skip().docID() <= B.docID():
                            A.doSkip()
                    else:
                        A_gagal.append( A.docID() )
                        A.next()
 
                else:
                        A.next()
            else:
                if B.hasSkip():
                    if B.skip().docID()<=A.docID() :
                        B_sukses.append( B.docID() )
                        while B.hasSkip() and B.skip().docID() <= B.docID() :
                            B.doSkip()
                    else:
                        B_gagal.append( B.docID() )
                        B.next()
                else:
                    B.next()
    print("A failed skips    :" + str(A_gagal) )
    print("A successful skips:" + str(A_sukses) )
    print("B failed skips    :" + str(B_gagal) )
    print("B successful skips:" + str(B_sukses) )
    return intersections
 
A = SkipList( [2,4,8,16,19,23,28,43]    )
B = SkipList( [1,2,3, 5, 8,41,51,60,71] )
 
print( "\nIntersections :" + str(INTERSECTWITHSKIPS(A,B) ) )