spawnv concatenates the arguments into a command line that gets passed to CreateProcessW in the lpCommandLine parameter. No shell is involved here. Unlike Python's subprocess.list2cmdline, the CRT's spawn family does not create a command line according to MSVC rules. It simply concatenates with spaces, which leaves it up to the caller to ensure that each argument is quoted and escaped according to the rules of the target application.

You can avoid the need to escape quotes in an argument by using only single quotes, which have no special meaning in MSVC argv parsing. For example: args = ['python', '-c', f'"{code}"'], where code contains no double quote characters.

There's no need for args[0] to be a fully-qualified path with spawnv. Actually, what you're doing by setting args[0] = sys.executable is wrong. It only works because the test build's path to "python.exe" contains no spaces. If the path has spaces and isn't quoted, then C argv[0] will only include up to the first space in the path, and the rest will be in argv[1], and so on. If you want to use the full path, it has to be quoted. For example, where sys.executable is "C:\Program Files\Python38\python.exe":

>>> os.spawnv(os.P_WAIT, sys.executable, [f'"{sys.executable}"', '-V'])
Python 3.8.1
0

Failing example without quoting:

>>> os.spawnv(os.P_WAIT, sys.executable, [sys.executable, '-V'])
C:\Program: can't open file 'Files\Python38\python.exe': [Errno 2] No such file or directory
2

Preferably, just use unqualified "python":

>>> os.spawnv(os.P_WAIT, sys.executable, ['python', '-V'])
Python 3.8.1
0