[ARROW-15053] [Python] Attribute nbytes of slice will return the value corresponding to the whole structure

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 6.0.0
• Fix Version/s: 7.0.0
• Component/s: Python
• External issue URL: https://github.com/apache/arrow/issues/30569
• Assignee: Vibhatha Lakmal Abeykoon
• Reporter: Adrien Hoarau
• Created: 10/Dec/21 12:42
• Updated: 11/Jan/23 08:44
• Resolved: 21/Apr/22 15:54

Description

Whether for tables/arrays, slicing and then calling `nbytes` will return the value for the whole struct. I don't know if this is a bug or the desired behaviour (and if it is I would argue that it should return a result relative to the slice, and also ask if there is any way to get the memory size of my slice?).

import pyarrow

pyarrow.__version__
>>> 6.0.0

table = pyarrow.Table.from_arrays([pyarrow.array(['foo', 'bar', 'qux'], type=pyarrow.string())], names=["a"])

table.num_rows
>>> 3

table.nbytes
>>> 25

table.slice(0, 2).num_rows
>>> 2

table.slice(0, 2).nbytes
>>> 25