best subsequence program in python code example

Example: python lcs length

def lcs(X, Y):
  
    n = len(Y)
    m = len(X)
    
    L = [[None]*(n + 1) for i in range(m + 1)]
    for i in range(m + 1): 
        for j in range(n + 1): 
            if i == 0 or j == 0 : 
                L[i][j] = 0
            elif X[i-1] == Y[j-1]: 
                L[i][j] = L[i-1][j-1]+1
            else: 
                L[i][j] = max(L[i-1][j], L[i][j-1])
                
    return L[m][n]