I do not know what "Linux" you are using.

    user@machine:~$ python3
    >>> with open('/tmp/a', 'wb') as f:
    ...     f.write (b'a'*1000);
    ... 
    1000
    >>> with open('/tmp/b', 'wb') as f:
    ...     f.write (b'a'*1024);
    ... 
    1024

    $ ll /tmp -h
    -rw-r--r-- 1 user user 1000 Feb  5 10:40 a
    -rw-r--r-- 1 user user 1.0K Feb  5 10:40 b