In [2]: old_var = np.arange(5)

In [3]: new_var = old_var

In [4]: old_var
Out[4]: array([0, 1, 2, 3, 4])

In [5]: new_var[0] = -1

In [6]: new_var
Out[6]: array([-1,  1,  2,  3,  4])

In [7]: old_var
Out[7]: array([-1,  1,  2,  3,  4])