code: def multiply(self, a, b):
      """
      :type A: List[List[int]]
      :type B: List[List[int]]
      :rtype: List[List[int]]
      """
      if a is None or b is None:
          return None
      m, n, l = len(a), len(b[0]), len(b[0])
      if len(b) != n:
          raise Exception(
              "A's column number must be equal to B's row number."
          )
      c = [[0 for _ in range(l)] for _ in range(m)]
      for i, row in enumerate(a):
          for k, eleA in enumerate(row):
              if eleA:
                  for j, eleB in enumerate(b[k]):
                      if eleB:
                          c[i][j] += eleA * eleB
      return c
  
label_desc: Use image node_id 1 for calling a global function with example usage: multiply(a, b) and returns: c, None