#defining the magic constants 

p=0xb7e15163
q=0x9e3779b9
pt=list()
pt1=list()
ct=list()
pt2=list()
#pt[0]=0pt1[0]=ct[0]=pt1[1]=ct[1]=0
s=[]
l=[]
b=8
key=[0,0,0,0,0,0,0,0,0]
w=8
t=16

def enc(c,d):
 for i in range(1,r):
  A=A+s[0]
  B=B+s[1]

  A=A^B
  A=str(A)
  B=str(B)
  A=A[len(B):]+A[:len(B)]

  B=B^A
  A=str(A)
  B=str(B)
  B=B[len(A):]+B[:len(B)]

  A=A+s[2*i]
  B=B+s[2*i+1]

 ct.append(A)
 ct.append(B)


def denc():
 for i in range(r,1):
  A=ct[0]
  B=ct[1]
  B=B-s[2*i+1]
  B=B[len(c):] + B[:len(c)]
  B=B^A

  A=A-s[2*i]
  A=A[:len(B)]+c[len(B):]
  A=A^B
 pt1[1]=B-S[1]
 pt1[0]=A-S[0]


def setup(k): 
 u=w/8 
 for i in range(b-1,0):
  l.append(l[i/u:8]+l[8:i/u]+k[i])
 s.append(p)
 for i in range(1,t-1):
  s.append(s[i-1] + q)

 i=j=0
 A=B=0
 for i in range(0,3*t):
  A=s.append(s[i]+A+B)
  B=s.append(s[:3]+s[3:])
  #B=l.append((l[j]+A+B))
  ll=len(str(A))+len(str(B))
  B=l.append(l[:ll]+l[ll:])
  i=(i+1)%t
  j=(j+1)%t




def pri(g):
 for k in range(0,w):
  print g & 0xFF


#for i in range(0,b):
 #key[i]=ct[0]%(255-j)
pt1=[raw_input()]
pt1=[raw_input()]
setup(key)
enc(pt1,ct)
denc(ct,pt2)

print("key")
print(key)
print("plaintext")

printword(pt1[0]),printword(pt1[1])
printword(ct[0]),printword(ct[1])

the list l is always going out of index though it should not . I am not able to take the length of the string A even though it is a string .Once i convert it to string i am not able to add it in s[j]+A+B. How to get around such errors and make the code more hygenic .. This is an rc5 cipher.