pty.spawn deadlock
Bug report
% yes | python3 -c "import pty; pty.spawn(['cat'])"
y
...
y^CTraceback (most recent call last):
File "<string>", line 1, in <module>
File "/usr/lib/python3.10/pty.py", line 181, in spawn
_copy(master_fd, master_read, stdin_read)
File "/usr/lib/python3.10/pty.py", line 161, in _copy
_writen(master_fd, data)
File "/usr/lib/python3.10/pty.py", line 127, in _writen
n = os.write(fd, data)
KeyboardInterrupt
You will see 2048 lines of y due to tty echo, then the output stops and hangs forever.
Both python and cat block on write, waiting each other consume something from pty buffer.
Your environment
Tested on Linux/macOS with CPython 3.10.