Python: Investigate enabling streaming output from ipykernel

[petetronic]

For use cases such as progress bar output, we don't see the progressive ANSI control characters, as ipykernel buffers output and sends the final state of the output instead.

We need to investigate ipykernel as to whether we can get it to stream output instead.

[softwarenerd]

For example, this does not work because progressive output is not being streamed:

from time import sleep
from alive_progress import alive_bar
for i in range(10):
    with alive_bar(100, ctrl_c=False, title=f'Download {i}') as bar:
        for i in range(100):
            sleep(0.02)
            bar()

[petetronic]

When we get to investigate this, we should consider if it is related to sys.stdout.isatty() returning False for our Python process.

[jmcphers]

Interestingly enough this does work for some kinds of progressive output. If you use pip install from inside Python, then pip streams progress bars to standard output, and they render beautifully during download and installation.

IPyKernel distinguishes between stdout text (which is streamed) and computational results from Python itself (which are not).

The reason output streaming "works" from R is that we treat everything as standard output, even intermediate computational results. This is itself a bug. See #281.

[seeM]

It looks like Jupyter Notebook has the same behavior as Positron with alive_bar.

Jupyter Notebook:

Screen.Recording.2024-02-07.at.14.54.03.mov

Positron Version: 2024.02.0 (Universal) build 1500:

Screen.Recording.2024-02-07.at.14.55.45.mov