How Do I Get The Address For An Element In A Python Array?

I'm a newbie and I'm trying to get the address of an element at a particular index in a Numpy or regular Python array. I'm following a class on Coursera where the instructor gets t

Solution 1:

An array and its attributes:

In [28]: arr = np.arange(1,8)
In [29]: arr.__array_interface__
Out[29]: 
{'data': (41034176, False),
 'strides': None,
 'descr': [('', '<i8')],
 'typestr': '<i8',
 'shape': (7,),
 'version': 3}

The data buffer location for a slice:

In[30]: arr[4:].__array_interface__['data'][0]Out[30]: 41034208In[31]: arr[4:].__array_interface__['data'][0]-arr.__array_interface__['data'][0]Out[31]: 32

The slice shares the data buffer, but with an offset of 4 elements (4*8).

Using this information I can fetch a slice using the ndarray constructor (not usually needed):

In [35]: np.ndarray((3,), dtype=int, buffer=arr.data, offset=32)
Out[35]: array([5, 6, 7])
In [36]: arr[4:7]
Out[36]: array([5, 6, 7])

---

arr.data is a memoryview object that somehow references the data buffer of this array. The id/address of arr.data is not the same as the data pointer I used above.

In [38]: arr.data
Out[38]: <memory at 0x7f996d950e88>
In [39]: type(arr.data)
Out[39]: memoryview

---

Note that data location for arr[4] is totally different. It is 'unboxed', not a slice:

In [37]: arr[4].__array_interface__
Out[37]: 
{'data': (38269024, False),
 'strides': None,
 'descr': [('', '<i8')],
 'typestr': '<i8',
 'shape': (),
 'version': 3,
 '__ref': array(5)}