The self object is somehow getting assigned value 1 and getting error while recurssion as 'int' object has no attribute 'seq1' (Solving LCS)

Question

I am trying to solve the longest common subsequence problem using recursion. I have written the following code for it. However I am encountering the same error each time and I am unable to make sense of it.

class LCS:

def __init__(self, seq1, seq2):
    self.seq1 = seq1
    self.seq2 = seq2
    
def recursive_LCS(self, index1 = 0, index2 = 0):
    # Terminating condition when either of the substring is empty
    if (self.seq1[index1:] == "") or (self.seq2[index2:] == ""):
        return 0
    # When first elements of the substrings match, we increase both the index by 1 
    elif self.seq1[index1] == self.seq2[index2]:
        return 1+ LCS.recursive_LCS(index1+1, index2+1)
    # When the first elements dont match, we split into two cases and choose the one with max matches
    else:
        return max(LCS.recursive_LCS(index1+1, index2), LCS.recursive_LCS(index1, index2+1))

str1 = "set"
str2 = "bet"
sub1 = LCS(str1, str2)
print(sub1.recursive_LCS())

This is the error message I am encountering

Exception has occurred: AttributeError'int' object has no attribute 'seq1'File "C:\Users\ACER\Desktop\Python Practice\test.py", line 10, in recursive_LCSif (self.seq1[index1:] == "") or (self.seq2[index2:] == ""):^^^^^^^^^File "C:\Users\ACER\Desktop\Python Practice\test.py", line 17, in recursive_LCSreturn max(LCS.recursive_LCS(index1+1, index2), LCS.recursive_LCS(index1, index2+1))^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^File "C:\Users\ACER\Desktop\Python Practice\test.py", line 22, in <module>print(sub1.recursive_LCS())^^^^^^^^^^^^^^^^^^^^AttributeError: 'int' object has no attribute 'seq1'

I am new to recursion and Object Oriented Approach hence i am unable to make any sense of what is resulting in this error, would really appreciate the help.

Answer 1

This problem is related to how you call: LCS.recursive_LCS(index1+1, index2). Your self here is index1+1 which is definitely not what you want. You should use self.recursive_LCS(index1+1, index2).

I've tested and it seems working!