DP Problem (Count distinct occurrences as a subsequence)

Given a two strings S and T, find count of distinct occurrences of T in S as a subsequence.

# Python3 program to count number of times 
# S appears as a subsequence in T 
def findSubsequenceCount(S, T):
m = len(T) 
n = len(S)
# T can't appear as a subsequence in S 
 if m > n: 
  return 0
# mat[i][j] stores the count of 
 # occurrences of T(1..i) in S(1..j). 
 mat = [[0 for _ in range(n + 1)] 
   for __ in range(m + 1)]
# Initializing first column with all 0s. x 
 # An empty string can't have another 
 # string as suhsequence 
 for i in range(1, m + 1): 
  mat[i][0] = 0
# Initializing first row with all 1s. 
 # An empty string is subsequence of all. 
 for j in range(n + 1): 
  mat[0][j] = 1
# Fill mat[][] in bottom up manner 
 for i in range(1, m + 1): 
  for j in range(1, n + 1):
# If last characters don't match, 
   # then value is same as the value 
   # without last character in S. 
   if T[i - 1] != S[j - 1]: 
    mat[i][j] = mat[i][j - 1] 
    
   # Else value is obtained considering two cases. 
   # a) All substrings without last character in S 
   # b) All substrings without last characters in 
   # both. 
   else: 
    mat[i][j] = (mat[i][j - 1] +
       mat[i - 1][j - 1])
return mat[m][n]