Why stdbuf has no effect on Python?

By default, Python's print() function directs its output to sys.stdout, whose documentation specifies this:

When interactive, stdout and stderr streams are line-buffered. Otherwise, they are block-buffered like regular text files. You can override this value with the -u command-line option.

Note well that those docs do not leave room for general environmental influences, such as that of the stdbuf command, on the buffering mode of sys.stdout: it is unbuffered if the -u option was used (or, equivalently, if environment variable PYTHONUNBUFFERED was set), otherwise line-buffered if interactive and block-buffered if non-interactive.

Programs can control their own buffering, as the docs of stdbuf acknowledge:

NOTE: If COMMAND adjusts the buffering of its standard streams ('tee' does for e.g.) then that will override corresponding settings changed by 'stdbuf'. Also some filters (like 'dd' and 'cat' etc.) don't use streams for I/O, and are thus unaffected by 'stdbuf' settings.

Since Python explicitly specifies buffering details, it is reasonable to expect that it in fact does affirmatively manage its buffering, thus mooting any effect of stdbuf.