[Python] How does subprocess.Popen works with shell=False on windows?

I'd like to understand how subprocess.Popen works on windows when shell=False. In particular, how is the environment or variable expansion taken into consideration by the underlying algorithm?

Consider the below simple test:

import os
import subprocess
import textwrap


def truncate(string, width):
if len(string) > width:
string = string[:width - 3] + '...'
return string


if __name__ == '__main__':
index = 0
commands = [
["where", "find.exe"],
"where find.exe",

[r"c:\windows\system32\where.exe", "find.exe"],
r"c:\windows\system32\where.exe find.exe",

["find.exe", "--version"],
"find.exe --version",

r"D:\sources\personal\sublimemerge\Git\usr\bin\find.exe --version",
]

def run(target, shell):
global index
label = (
f'{index:<2}) subprocess.run('
f'{repr(target)}, shell={shell}, '
f'stdout=subprocess.PIPE, stderr=subprocess.STDOUT, '
f'universal_newlines=True)'
)
label = f"{label:<160}"

try:
x = subprocess.run(target, shell=shell, stdout=subprocess.PIPE,
stderr=subprocess.STDOUT, universal_newlines=True)
print(f"{label} - returncode={x.returncode} - {repr(truncate(x.stdout, 40))}")
except Exception as e:
print(f"{label} - exception={repr(truncate(str(e), 90))}")

index += 1

for c in commands:
run(c, shell=True)
run(c, shell=False)


Where the output looks like this:

0 ) subprocess.run(['where', 'find.exe'], shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True) - returncode=0 - 'D:\\sources\\personal\\sublimemerge\\Git\\...'
1 ) subprocess.run(['where', 'find.exe'], shell=False, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True) - returncode=0 - 'D:\\sources\\personal\\sublimemerge\\Git\\...'
2 ) subprocess.run('where find.exe', shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True) - returncode=0 - 'D:\\sources\\personal\\sublimemerge\\Git\\...'
3 ) subprocess.run('where find.exe', shell=False, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True) - returncode=0 - 'D:\\sources\\personal\\sublimemerge\\Git\\...'
4 ) subprocess.run(['c:\\windows\\system32\\where.exe', 'find.exe'], shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True) - returncode=0 - 'D:\\sources\\personal\\sublimemerge\\Git\\...'
5 ) subprocess.run(['c:\\windows\\system32\\where.exe', 'find.exe'], shell=False, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True) - returncode=0 - 'D:\\sources\\personal\\sublimemerge\\Git\\...'
6 ) subprocess.run('c:\\windows\\system32\\where.exe find.exe', shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True) - returncode=0 - 'D:\\sources\\personal\\sublimemerge\\Git\\...'
7 ) subprocess.run('c:\\windows\\system32\\where.exe find.exe', shell=False, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True) - returncode=0 - 'D:\\sources\\personal\\sublimemerge\\Git\\...'
8 ) subprocess.run(['find.exe', '--version'], shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True) - returncode=0 - 'find (GNU findutils) 4.6.0\nCopyright ...'
9 ) subprocess.run(['find.exe', '--version'], shell=False, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True) - returncode=2 - 'FIND: Parameter format not correct\n'
10) subprocess.run('find.exe --version', shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True) - returncode=0 - 'find (GNU findutils) 4.6.0\nCopyright ...'
11) subprocess.run('find.exe --version', shell=False, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True) - returncode=2 - 'FIND: Parameter format not correct\n'
12) subprocess.run('D:\\sources\\personal\\sublimemerge\\Git\\usr\\bin\\find.exe --version', shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True) - returncode=0 - 'find (GNU findutils) 4.6.0\nCopyright ...'
13) subprocess.run('D:\\sources\\personal\\sublimemerge\\Git\\usr\\bin\\find.exe --version', shell=False, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True) - returncode=0 - 'find (GNU findutils) 4.6.0\nCopyright ...'


The first question that comes to my mind would be, why do I need to specify the full executable path when shell=False? Why is env not considered the same way than when shell=True is used? Actually... look at cases 5,7, by just looking at those one would think env is being taken into consideration.

I guess the whole matter boils down to understand how env is given to CreateProcess call in cpython's _winapi.c.

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