subprocess: error redirecting i/o from non-console process

[orenti]

BPO	1603907
Files	subprocess-noconsole.patch: fix redirection in non-console processes subprocess-noconsole2.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2007-01-22.19:29:10.000>
created_at = <Date 2006-11-27.17:20:38.000>
labels = []
title = 'subprocess: error redirecting i/o from non-console process '
updated_at = <Date 2007-01-22.19:29:10.000>
user = 'https://bugs.python.org/orenti'

bugs.python.org fields:

activity = <Date 2007-01-22.19:29:10.000>
actor = 'astrand'
assignee = 'astrand'
closed = True
closed_date = None
closer = None
components = ['None']
creation = <Date 2006-11-27.17:20:38.000>
creator = 'orenti'
dependencies = []
files = ['2243', '2244']
hgrepos = []
issue_num = 1603907
keywords = []
message_count = 6.0
messages = ['30701', '30702', '30703', '30704', '30705', '30706']
nosy_count = 2.0
nosy_names = ['astrand', 'orenti']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1603907'
versions = ['Python 2.5']

[orenti]

In IDLE, PythonWin or other non-console interactive Python under Windows:

>> from subprocess import *
>> Popen('cmd', stdout=PIPE)

Traceback (most recent call last):
  File "<pyshell#11>", line 1, in -toplevel-
    Popen('', stdout=PIPE)
  File "C:\python24\lib\subprocess.py", line 533, in __init__
    (p2cread, p2cwrite,
  File "C:\python24\lib\subprocess.py", line 593, in _get_handles
    p2cread = self._make_inheritable(p2cread)
  File "C:\python24\lib\subprocess.py", line 634, in _make_inheritable
    DUPLICATE_SAME_ACCESS)
TypeError: an integer is required

The same command in a console windows is successful.

Why it happens:
subprocess assumes that GetStdHandle always succeeds but when there is no console it returns None. DuplicateHandle then complains about getting a non-integer. This problem does not happen when redirecting all three standard handles.

Solution:
Replace None with -1 (INVALID_HANDLE_VALUE) in _make_inheritable.

Patch attached.

[astrand]

This patch looks very interesting. However, it feels a little bit strange to call DuplicateHandle with a handle of -1. Is this really allowed? What will DuplicateHandle return in this case? INVALID_HANDLE_VALUE? In that case, isn't it better to return INVALID_HANDLE_VALUE directly?

[orenti]

If you duplicate INVALID_HANDLE_VALUE you get a new valid handle to nothing :-) I guess the code really should not rely on this undocumented behavior. The reason I didn't return INVALID_HANDLE_VALUE directly is because DuplicateHandle returns a _subprocess_handle object, not an int. It's expected to have a .Close() method elsewhere in the code.

Because of subtle difference between in the behavior of the _subprocess and win32api implementations of GetStdHandle in this case solving this issue this gets quite messy!
File Added: subprocess-noconsole2.patch

[orenti]

Oops. The new patch does not solve it in all cases in the win32api version, either...

[astrand]

This the suggested patches are not ready for commit, I'm moving this issue to "bugs" instead.

[astrand]

Duplicate of 1124861.