Hi,

I am experimenting with variable length attributes using Python bindings. I am experiencing some unexpected behaviors. For instance, if all the subarrays have the same length, I get a buffer conversion error.

```
# Array creation
ctx = tiledb.default_ctx()
dim = tiledb.Dim(name="dimension", domain=(0, 10000), tile=100, dtype=np.int64)
domain = tiledb.Domain(dim)
attr = tiledb.Attr(name="attr", dtype=np.int64, var=True)
schema = tiledb.ArraySchema(domain=domain, sparse=False, attrs=[attr])
tiledb.Array.create(array_path, schema, overwrite=True)
```

```
# fails if all subarrays have the same length here
x = [
np.array([0,1,2,3], dtype=np.int64),
np.array([0,1,2,3], dtype=np.int64),
]
with tiledb.open(array_path, 'w') as A:
A[0 : len(x)] = np.array(x, dtype='O')
```

And then I get `TileDBError: Failed to convert buffer for attribute: 'attr'`

.

But, even if one sub-array has a different size, it works.

And also if only one sub-array is provided, regardless of its content, I get the same buffer conversion error.

```
# fails
x = [
np.array([0,1,2,3], dtype=np.int64)
]
with tiledb.open(array_path, 'w') as A:
A[0 : len(x)] = np.array(x, dtype='O')
```

Am I missing something here or maybe it is a bug?

Thanks.