[issue30783] Spawned subprocesses don't respect environment

[Eryk Sun]

Eryk Sun added the comment:

cmd.exe implements its own search, like shutil.which, and uses the 
CreateProcess lpApplicationName parameter that corresponds to the Popen 
executable parameter. But in general (not always) it's better to use 
shutil.which because you don't have to worry about the security problems that 
come with using the shell.

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[issue30783] Spawned subprocesses don't respect environment

[Ofek Lev]

Ofek Lev added the comment:

Fixed with shell=True

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[issue30783] Spawned subprocesses don't respect environment

[Eryk Sun]

Eryk Sun added the comment:

subprocess.Popen calls CreateProcess on Windows, which searches for an 
unqualified executable in the command line as follows:

1. The directory from which the application loaded.
2. The current directory for the parent process. (Starting with
   Vista, the current directory is excluded from this search if
   the environment variable NoDefaultCurrentDirectoryInExePath is
   defined.)
3. The 32-bit Windows system directory. Use the GetSystemDirectory
   function to get the path of this directory.
4. The 16-bit Windows system directory. There is no function that
   obtains the path of this directory, but it is searched. The
   name of this directory is System.
5. The Windows directory. Use the GetWindowsDirectory function to
   get the path of this directory.
6. The directories that are listed in the PATH environment
   variable.

Thus searching for "python" will always find "python.exe" from the application 
directory. 

To work around this, you can use shutil.which() to find python.exe on PATH and 
pass it as the `executable` argument. For example:

os.environ['PATH'] = ';'.join([r'C:\Program Files\Python35', old_path])
python35 = shutil.which('python')

>>> print(python35)
C:\Program Files\Python35\python.EXE

>>> _ = subprocess.call('python -V')
Python 3.6.1

>>> _ = subprocess.call('python -V', executable=python35)
Python 3.5.2

--
nosy: +eryksun
resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue30783] Spawned subprocesses don't respect environment

[Ofek Lev]

New submission from Ofek Lev:

The following example shows that we are indeed changing PATH, but the 
subprocess does not acknowledge it in Windows 7 x64. Also note this works in 
Linux (Ubuntu 16.04).

-

import os
import subprocess
from contextlib import contextmanager
from tempfile import TemporaryDirectory


def get_python_path():
return subprocess.check_output(
['python', '-c', 'import sys;print(sys.executable)']
).decode().strip()


@contextmanager
def temp_chdir(cwd=None):
with TemporaryDirectory() as d:
origin = cwd or os.getcwd()
os.chdir(d)

try:
yield d
finally:
os.chdir(origin)


def create_venv(d, pypath=None):
command = ['virtualenv', d]
if pypath:
command.extend(['-p', pypath])
subprocess.call(command)


@contextmanager
def venv(d):
if os.path.exists(os.path.join(d, 'bin')):  # no cov
venv_exe_dir = os.path.join(d, 'bin')
elif os.path.exists(os.path.join(d, 'Scripts')):
venv_exe_dir = os.path.join(d, 'Scripts')
else:
raise OSError('Unable to locate executables directory.')

old_path = os.environ['PATH']
os.environ['PATH'] = '{}{}{}'.format(venv_exe_dir, os.pathsep, old_path)
yield
os.environ['PATH'] = old_path


def test_venv():
with temp_chdir() as d:
d = os.path.join(d, 'test_env')
create_venv(d)
global_python = get_python_path()
print('PATH', os.environ['PATH'][:140])

with venv(d):
print('PATH', os.environ['PATH'][:140])
venv_python = get_python_path()

assert global_python != venv_python
assert global_python == get_python_path()

--
components: Windows
messages: 296986
nosy: Ofekmeister, paul.moore, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
status: open
title: Spawned subprocesses don't respect environment
type: behavior
versions: Python 3.6

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