objectif

Empiler des context managers conditionnels proprement.

code minimal

from contextlib import ExitStack
from tempfile import TemporaryDirectory, NamedTemporaryFile
from pathlib import Path

with ExitStack() as stack:
    tmpdir = stack.enter_context(TemporaryDirectory())
    tmpf = stack.enter_context(NamedTemporaryFile(delete=False))
    p = Path(tmpdir) / "x.txt"
    p.write_text("ok", encoding="utf-8")
    print(p.exists() and Path(tmpf.name).exists())  # attendu: True

utilisation

from contextlib import ExitStack
def maybe_open(path, enable: bool, stack: ExitStack):
    if enable:
        return stack.enter_context(open(path, "w", encoding="utf-8"))
    return None
with ExitStack() as st:
    f = maybe_open("out.txt", False, st)
    print(f is None)

variante(s) utile(s)

from contextlib import ExitStack
with ExitStack() as st:
    callbacks = []
    st.callback(lambda: callbacks.append("done"))
print(callbacks == ["done"])

notes

• exitstack permet d’enregistrer contextes et callbacks dynamiquement.
• Idéal pour ressources optionnelles (fichiers, verrous, connexions).