distutils: find_executable() fails if the PATH environment variable is not set

[vstinner]

BPO	34530
Nosy	@pfmoore, @ncoghlan, @vstinner, @serhiy-storchaka, @dstufft, @miss-islington
PRs	bpo-34530: Fix distutils find_executable() #8968 bpo-34530: Fix distutils find_executable() #9049 [3.7] bpo-34530: Fix distutils find_executable() (GH-9049) #9056 [3.6] bpo-34530: Fix distutils find_executable() (GH-9049) #9057 [2.7] bpo-34530: Fix distutils find_executable() (GH-9049) #9058 [3.6] bpo-34530: Fix distutils find_executable() (GH-9049) #9071

^{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 2018-09-05.14:48:46.462>
created_at = <Date 2018-08-28.12:47:31.571>
labels = ['3.8', '3.7', 'library']
title = 'distutils: find_executable() fails if the PATH environment variable is not set'
updated_at = <Date 2018-09-05.14:48:46.442>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2018-09-05.14:48:46.442>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2018-09-05.14:48:46.462>
closer = 'vstinner'
components = ['Library (Lib)']
creation = <Date 2018-08-28.12:47:31.571>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 34530
keywords = ['patch']
message_count = 10.0
messages = ['324245', '324246', '324380', '324381', '324539', '324566', '324575', '324578', '324636', '324640']
nosy_count = 7.0
nosy_names = ['paul.moore', 'ncoghlan', 'vstinner', 'serhiy.storchaka', 'dstufft', 'Marcus.Smith', 'miss-islington']
pr_nums = ['8968', '9049', '9056', '9057', '9058', '9071']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue34530'
versions = ['Python 2.7', 'Python 3.6', 'Python 3.7', 'Python 3.8']

[vstinner]

Example:

$ env -i ./python -c 'import distutils.spawn; print(distutils.spawn.find_executable("true"))'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/vstinner/prog/python/master/Lib/distutils/spawn.py", line 176, in find_executable
    path = os.environ['PATH']
  File "/home/vstinner/prog/python/master/Lib/os.py", line 672, in __getitem__
    raise KeyError(key) from None
KeyError: 'PATH'

Attached PR fixes the issue for the master branch.

[vstinner]

I'm not sure that it's worth it to modify Python 3.7 and older. distutils changes are now well welcomed (breaking setuptools or pip is unpopular :-)).

[serhiy-storchaka]

find_executable() always searches executables from the current directory. This effectively equivalent having os.curdir at the start of path. shutil.which() does this only on Windows. This change LGTM, but it potentially can break user code, thus it may be not safe to make it in maintained versions.

[vstinner]

find_executable() always searches executables from the current directory.

Oh! I didn't notice that!

[vstinner]

I missed the fact that find_executable() always lookup in the current directory, whereas shutil.which() doesn't. I abandoned my PR 8968 in favor of PR 9049 which only fix the case where PATH env var is not defined. This PR can easily be backported to all branches, whereas backporting PR 8968 to stable branches would be risky: changes to distutils are likely to break a random package on PyPI.

[vstinner]

New changeset 3948719 by Victor Stinner in branch 'master':
bpo-34530: Fix distutils find_executable() (GH-9049)
3948719

[miss-islington]

New changeset 7aa3ead by Miss Islington (bot) in branch '3.7':
bpo-34530: Fix distutils find_executable() (GH-9049)
7aa3ead

[vstinner]

New changeset 7056ca8 by Victor Stinner in branch '2.7':
bpo-34530: Fix distutils find_executable() (GH-9049) (GH-9058)
7056ca8

[vstinner]

New changeset e2c1657 by Victor Stinner (Miss Islington (bot)) in branch '3.6':
bpo-34530: Fix distutils find_executable() (GH-9049) (GH-9057)
e2c1657

[vstinner]

I chose to merge the simplest change:

•    path = os.environ['PATH']
  

+ path = os.environ.get('PATH', os.defpath)

And I added unit tests for find_executable(). The bug is now fixed.

I'm not longer interested to reuse shutil.which() in distutils.find_executable(), since find_executable() first checks if the executable is in the current directory.