shutil imports bz2/lzma/zstd at startup just to check they exist
shutil imports bz2, lzma and compression.zstd at module scope purely to discover whether those formats are available, then throws the bindings away:
try:
import bz2
del bz2
_BZ2_SUPPORTED = True
except ImportError:
_BZ2_SUPPORTED = FalseEvery program importing shutil pays for that, even if it never creates or extracts an archive and shutil is imported transitively by much of the stdlib: on main, each of urllib.request, tempfile, zipfile, tarfile, http.server and venv ends up with shutil in sys.modules.
Net import cost (median of 40 fresh interpreters):
|
net cost |
import shutil |
12.75 ms |
import urllib.request |
36.64 ms |
This matters most for short-lived processes on constrained hardware: CLI tools and serverless cold starts, where a few ms per process is worth removing.
I have a patch with tests that cuts this by ~2.5 ms (−19.6%) on import shutil, and will open a PR.
Linked PRs
shutilimports bz2/lzma/zstd at startup just to check they existshutilimportsbz2,lzmaandcompression.zstdat module scope purely to discover whether those formats are available, then throws the bindings away:Every program importing
shutilpays for that, even if it never creates or extracts an archive andshutilis imported transitively by much of the stdlib: onmain, each ofurllib.request,tempfile,zipfile,tarfile,http.serverandvenvends up withshutilinsys.modules.Net import cost (median of 40 fresh interpreters):
import shutilimport urllib.requestThis matters most for short-lived processes on constrained hardware: CLI tools and serverless cold starts, where a few ms per process is worth removing.
I have a patch with tests that cuts this by ~2.5 ms (−19.6%) on
import shutil, and will open a PR.Linked PRs