[Python] subclass numpy arrays: when using resize, how to re-attach the view to sliced...

I am trying to create a buffer array that creates extra indexes of the numpy so I can assign rather than using functions like np.append and where "children" sliced array can still be a view from the parent. My code below can do this, but I also want to include the functionality such that when self.resize() is called on the parent array, it will trigger a callback that will send the parent back to the child and "re-attach" the parent to the child.

From the code below, we can see that the child's memory address has changed, but it's not the same as the parent's. I tried slicing the parent into the child (child[:] = parent[child.idx:], but he error ValueError: cannot resize this array: it does not own its data

Is there anyway to do this?

class BufferArray(np.ndarray):
GROWTH = 2
def __new__(cls, input_array):
base = np.asarray(input_array, dtype=float)
n = base.size
cap = max(1, 2 * n)
obj = super().__new__(cls, shape=(cap,), dtype=base.dtype)
obj[:n] = base
obj[n:] = np.nan
obj.n = n
return obj

def __array_finalize__(self, obj):
if obj is None:
return
self.n = getattr(obj, "n", 0)

def _grow(self):
old = self.size
self.resize(old * self.GROWTH, refcheck=False)
self[old:] = np.nan
if getattr(self, "mirror_callbacks", False):
if len(self.mirror_callbacks) > 0:
for callback in list(self.mirror_callbacks):
callback(self)

def update_value(self, value):
if self.n >= self.size:
self._grow()
self[self.n] = value
self.n += 1

def _attach_mirror(self, mirror):
print(f"\n_attach_mirror called")
print(f"parent id: {id(mirror)}")
print(f"child id before: {id(self)}")
#self._grow() # returns ValueError: cannot resize this array: it does not own its data
#self[:] = mirror[self.mirror_idx:] # returns ValueError: cannot resize this array: it does not own its data
self = mirror.create_mirror(self.mirror_idx)
print(f"child id after: {id(self)}")

def _add_mirror_callbacks(self, callback):
if not getattr(self, "mirror_callbacks", False):
self.mirror_callbacks=[callback]
else:
self.mirror_callbacks.append(callback)

def create_mirror(self, idx):
slice = self[idx:]
slice.mirror_idx = idx
self._add_mirror_callbacks(slice._attach_mirror)
return slice

parent = BufferArray(np.zeros(2, dtype=int))
child = parent.create_mirror(1)

print(f"parent id: {id(parent)}")
print(f"child id: {id(child)}")
print(f"parent: {parent}")
print(f"child: {child}")

print(f"\nlooping")
for i in range(1, 4):
parent.update_value(10*i)
print("\n")
print(f"parent: {parent}")
print(f"parent.n: {parent.n}")
print(f"child: {child}")
print(f"child.n: {child.n}")

print(f"\nfinal")
print(f"parent: {parent}")
print(f"child: {child}")

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