dtype属性代表array中数据的类型，可以是int，float，str等

a.dtype

dtype('int32')

dtype属性的修改不可以直接进行，而应该借助于astype()方法

a.dtype = "float64"

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

ValueError                                Traceback (most recent call last)

<ipython-input-18-a4cdf5bd3aee> in <module>()
----> 1 a.dtype = "float64"


ValueError: When changing to a larger dtype, its size must be a divisor of the total size in bytes of the last axis of the array.

a = a.astype(np.float64)
print(a)
print(a.dtype)

[[[ 0.  1.  2.  3.  4.]
  [ 5.  6.  7.  8.  9.]]

 [[10. 11. 12. 13. 14.]
  [15. 16. 17. 18. 19.]]]
float64