bug: Python integration buffering issue

[aofei]

Description

There is a bug in the Python integration that needs to be addressed.

When running the following command:

llgo run ./_pydemo/callpy/

The output is displayed correctly. However, when running:

llgo run ./_pydemo/callpy/ > output.txt && cat output.txt

There is no output.

Root cause

The root cause of this issue appears to be related to Python's default buffering mode. By default, Python uses buffered I/O for sys.stdin, sys.stdout, and sys.stderr.

• In the 1st case, the output is shown in the console because it uses line buffering.
• In the 2nd case, the output is not captured in output.txt because it uses full buffering, and the buffer is not flushed before the program exits.

Workarounds

The issue can be temporarily fixed by disabling Python's buffering mode manually:

export PYTHONUNBUFFERED=1

Possible solutions

To resolve this issue in llgo,

• it may be necessary to switch Python to unbuffered mode;
• or provide a manual flush option, though this could be cumbersome for users;
• or ensure the buffer is flushed before the program exits to retain Python's default design.

For reference, Go's os.Stdin, os.Stdout, and os.Stderr are always unbuffered (see: golang-nuts).