return None instead of 0 in GetStdHandle

[slozier]

Resolves an issue reported on gitter by @danabr:

Hi. I have a mysterious issue with subprocess.Popen with stdout=subprocess.PIPE. It works fine from the IronPython console, and also when I run IronPython2 embedded in my application. However, when I use embedded IronPython3, I get: OSError: [WinError 6] The handle is invalid. Here is a stacktrace:

File "myscript.py", line 137, in main
    p = subprocess.Popen(commands, shell=True, stdout=subprocess.PIPE)
  File "lib\subprocess.py", line 833, in __init__
    (p2cread, p2cwrite,
  File "lib\subprocess.py", line 1033, in _get_handles
    p2cread = self._make_inheritable(p2cread)
  File "lib\subprocess.py", line 1080, in _make_inheritable
    h = _winapi.DuplicateHandle(

The issue only occurs when I the stdin argument is not supplied or is set to None. The code in subprocess.py then tries to get the default stdin handle with _winapi.GetStdHandle(_winapi.STD_INPUT_HANDLE). That call returns 0 in this case.

The code then goes on to compare the result with None, which seems wrong. From the docs of GetStdHandle:

If an application does not have associated standard handles, such as a service running on an interactive desktop, and has not redirected them, the return value is NULL.

[slide]

Is this change really needed for the _winapi stuff?

[slide]

nm, I see now

[slozier]

I just wanted the green checkmark so I snuck it in. 😄