bpo-35537: subprocess can now use os.posix_spawnp by vstinner · Pull Request #11579 · python/cpython

Please keep in mind that _posixsubprocess is likely to use a different algorithm for searching in PATH compared to posix_spawnp implementations (and, moreover, posix_spawnp implementations differ between libcs and even between versions of the same libc). For example, musl uses execvpe as a "backend" for posix_spawnp, which skips only 3 kinds of errors, while _posixsubprocess skips all errors. Also, EACCES is treated in a special way by both glibc and musl.

Also, the default PATH if the environment variable is not set is likely to differ (e.g., glibc uses /bin:/usr/bin, musl uses /usr/local/bin:/bin:/usr/bin, and Python uses :/bin:/usr/bin).