On Windows, Python 3.3.2, when I run Python as a subprocess via Popen("py -i somescript.py", stdin=PIPE, stdout=PIPE, stderr=PIPE).communicate() and somescript.py ends with exception, there is first interactive promt ">>>" in stderr output and then the traceback which is reversed to standard order when somescript.py is run interactively directly.

Corresponding StackOverflow question: http://stackoverflow.com/questions/18419724/position-of-prompt-in-stderr-after-systemexit .

For anyone who wants to look in to this: according to the stack overflow question and comments, this is a behavior change between python2 and python3.

Yes, it is a behavior change between Python 2 and Python 3. I just tried with 2.7 and 3.0.

On version 3.10, windows 10 I don't see this - the prompt comes after the traceback.

Adam, are you seeing this issue on any python version >= 3.8?

So far I could reproduce the issue on Python 3.7, Windows Vista 64bit. I'll try with newer versions.

The output I got:
>>> from subprocess import *
>>> Popen("py -i foo.py", stdin=PIPE, stdout=PIPE, stderr=PIPE).communicate()
(b'', b'>>> Traceback (most recent call last):\r\n  File "foo.py", line 2, in <module>\r\n    1/0\r\nZeroDivisionError: division by zero\r\n\r\n')

The order is fine on Python 3.8, Windows 10.

Thanks. I'm closing this because 3.7 is only getting security fixes now.