posix_spawn explicit file_actions=None throws error

[MatthewTanous]

BPO	36814
Nosy	@vstinner, @tonybaloney, @nanjekyejoannah
PRs	bpo-36814: ensure os.posix_spawnp handles Py_None #13144

^{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 = 'https://github.com/tonybaloney'
closed_at = <Date 2019-05-10.02:01:01.766>
created_at = <Date 2019-05-06.15:05:56.265>
labels = ['3.8', 'library']
title = 'posix_spawn explicit file_actions=None throws error'
updated_at = <Date 2019-05-10.02:01:01.766>
user = 'https://bugs.python.org/MatthewTanous'

bugs.python.org fields:

activity = <Date 2019-05-10.02:01:01.766>
actor = 'vstinner'
assignee = 'anthonypjshaw'
closed = True
closed_date = <Date 2019-05-10.02:01:01.766>
closer = 'vstinner'
components = ['Library (Lib)']
creation = <Date 2019-05-06.15:05:56.265>
creator = 'Matthew Tanous'
dependencies = []
files = []
hgrepos = []
issue_num = 36814
keywords = ['patch']
message_count = 7.0
messages = ['341522', '341659', '341661', '341663', '341664', '342036', '342038']
nosy_count = 4.0
nosy_names = ['vstinner', 'Matthew Tanous', 'anthonypjshaw', 'nanjekyejoannah']
pr_nums = ['13144']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue36814'
versions = ['Python 3.8']

[MatthewTanous]

Allowing posix_spawn file_actions to default to None works, but explicitly setting it throws a TypeError:

Python 3.8.0a3 (v3.8.0a3:9a448855b5, Mar 25 2019, 17:05:20)
[Clang 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> os.posix_spawnp('whoami', ['whoami'], os.environ, file_actions=None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: file_actions must be a sequence or None

This required me to default to an empty sequence to complete it:

>>> os.posix_spawnp('whoami', ['whoami'], os.environ, file_actions=[])
6308

[tonybaloney]

Verified on master
Python 3.8.0a3+ (heads/bpo-28367:373c7aa098, May  6 2019, 17:34:39) 
[Clang 10.0.1 (clang-1001.0.46.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> os.posix_spawnp('whoami', ['whoami'], os.environ, file_actions=None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'os' is not defined
>>> import os
>>> os.posix_spawnp('whoami', ['whoami'], os.environ, file_actions=None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: file_actions must be a sequence or None

[tonybaloney]

Issue is in parse_file_actions

parse_file_actions(PyObject *file_actions,
                   posix_spawn_file_actions_t *file_actionsp,
                   PyObject *temp_buffer)
{
    PyObject *seq;
    PyObject *file_action = NULL;
    PyObject *tag_obj;

    seq = v(file_actions,
                          "file_actions must be a sequence or None");
    if (seq == NULL) {
        return -1;
    }

PySequence_Fast will raise a TypeError if PyObject_GetIter fails.

[tonybaloney]

Raised a fix in #57353

[tonybaloney]

After patch:

Python 3.8.0a3+ (heads/31968-dirty:c664b342a4, May  6 2019, 18:06:21) 
[Clang 10.0.1 (clang-1001.0.46.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.posix_spawnp('whoami', ['whoami'], os.environ, file_actions=None)
17300
>>> anthonyshaw

[vstinner]

New changeset 948ed8c by Victor Stinner (Anthony Shaw) in branch 'master':
bpo-36814: ensure os.posix_spawn() handles None (GH-13144)
948ed8c

[vstinner]

Matthew Tanous: Oops, I completely missed this case! Thanks for the bug report.

Thanks Anthony Shaw for the fix.