Python 3 function to calculate optimal buffer size for any io.BufferedIOBase subclass, like io.BufferedReader and io.BufferedWriter

buffered_io_get_buffer_size.py

"""
===============================
BufferedIOBase Buffer Size Calculator
===============================

This Python script contains a function `buffio_get_buffsz` that calculates
the buffer size of a `BufferedIOBase` object.

Functionality
=============

The function `buffio_get_buffsz` takes a `BufferedIOBase` object as input and
returns the buffer size of the object. The buffer size is calculated by
rounding down the size of the object to the nearest power of 2. The size of
the object is obtained using the `sys.getsizeof()` function with a default
buffer size.

Usage
=====

Import the function into your Python script and pass a `BufferedIOBase` object
to it. The function will return the buffer size of the object.

.. code-block:: python

    # Create a BufferedIOBase object
    fileobj = io.BufferedReader(io.BytesIO(b"Hello World"))

    # Get the buffer size
    buffer_size = buffio_get_buffsz(fileobj)
    print(f"The buffer size is {buffer_size}")

Source
======

This function is based on a gist available at:
https://gist.github.com/rindeal/583ce8f34d155c782c838ff2ec788940
"""

import io
import sys


def buffio_get_buffsz(fileobj: io.BufferedIOBase) -> int:
    """
    Calculate the real buffer size of a BufferedIOBase object.

    This function calculates the buffer size of a BufferedIOBase object by rounding down the size of the object to the nearest power of 2. 
    The size of the object is obtained using the sys.getsizeof() function with a default buffer size.

    Source:
    https://gist.github.com/rindeal/583ce8f34d155c782c838ff2ec788940

    Parameters:
    fileobj (io.BufferedIOBase): The BufferedIOBase object for which the buffer size is to be calculated.

    Returns:
    int: The buffer size of the BufferedIOBase object.

    """
    def round_down_to_pow2(n: int) -> int:
        return 1 << (n.bit_length() - 1) if n != 0 else 0
    return round_down_to_pow2(sys.getsizeof(fileobj, io.DEFAULT_BUFFER_SIZE))