list append / extend return None

import copy
x1 = [1,2]
x2 = [3,4]
x3 = [[5],[6]]

----------------------------------------
q1 = [x.append(b) for x in x3 for b in x1]
print(q1)

# return [None,None,None,None]

----------------------------------------

q2 = [copy.deepcopy(x).append(b) for x in x3 for b in x1]
print(q2)

# return [None,None,None,None]

----------------------------------------

tmp_x_list = []
for x in x1:
      for w2 in x3:
            x2_c = copy.deepcopy(w2)
            x2_c.append(x)
            tmp_x_list.append(x2_c)
print(tmp_x_list)

return [[5, 1], [6, 1], [5, 2], [6, 2]]

----------------------------------------

list 的append / extend均 return None，真他娘血的教训