import numpy as np

a = np.array([[[1,1,1,1,1], [2,3,4,5,6]], [[1,1,1,1,1], [2,3,4,5,6]]])
b = np.sum(a, axis = -1)  # axis: -1 代表最後一維
b = b.reshape([2, 2, 1])  # a 與 b 需要維度相同才能做除法運算
c = a / b

print(a, end="\n\n")
print(b, end="\n\n")
print(c, end='\n\n')

result:
[[[1 1 1 1 1]
  [2 3 4 5 6]]

 [[1 1 1 1 1]
  [2 3 4 5 6]]
 
]

[[[ 5]
  [20]]

 [[ 5]
  [20]]]

[[[0.2  0.2  0.2  0.2  0.2 ]
  [0.1  0.15 0.2  0.25 0.3 ]]

 [[0.2  0.2  0.2  0.2  0.2 ]
  [0.1  0.15 0.2  0.25 0.3 ]]]

參考

import numpy as np

a = np.array([[[0,0,0,0,0], [0,0,0,0,0]], [[0,0,0,0,0], [0,0,0,0,0]]])
b = np.sum(a, axis = -1)  # axis: -1 代表最後一維
b = b.reshape([2, 2, 1])  # a 與 b 需要維度相同才能做除法運算

with np.errstate(divide='ignore'
 
, invalid='ignore'):  # 防止提示 Warning
    d, c = a / b, a / b
    c[ ~ np.isfinite( c )] = 0  # 防止出現Nan, 使得 0/0 = 0

print(d, end='\n\n')
print(c, end='\n\n')

results:
[[[nan nan nan nan nan]
  [nan nan nan nan nan]]

 [[nan nan nan nan nan]
  [nan nan nan nan nan]]]

[[[0. 0. 0. 0. 0.]
  [0. 0. 0. 0. 0.]]

 [[0. 0. 0. 0. 0.]
  [0. 0. 0. 0. 0.]]
 
]