numpy array に対する通常の代入操作は，いわばリンクをつくるだけで実体はひとつなので，代入後のnumpy arrayを新しいメモリ上にとるためには，copyを使う必要がある．
>a=np.array([1,2,3])
>b=a
>c=a.copy()
>a[0]=10 # An element of a is changed.
>a
array([10, 2, 3])
>b
array([10, 2, 3]) # The element of b, produced by a substitution, is also changed.
>c
array([1, 2, 3]) # The element of c, produced by copy, is not changed.
リストにはimport copy をして，copy.copyを，辞書などにはcopy.deepcopyを使って，新しい実体を作ることができる．
The substitution operation to numpy array produces a "link" that refers the same memory. If you want to produce a numpy array, disconnected from the original one, you need to use copy command.
>a=np.array([1,2,3])
>b=a
>c=a.copy()
>a[0]=10 # An element of a is changed.
>a
array([10, 2, 3])
>b
array([10, 2, 3]) # The element of b, produced by a substitution, is also changed.
>c
array([1, 2, 3]) # The element of c, produced by copy, is not changed.
To produce a new list (dictionary), you can use copy.copy (deepcopy.copy).