objectif

Accéder à des segments de fichier sans tout charger en mémoire.

code minimal

import mmap, tempfile, os

with tempfile.NamedTemporaryFile(delete=False) as f:
    f.write(b"0123456789"*100)
    path = f.name

with open(path, "r+b") as f:
    with mmap.mmap(f.fileno(), length=0, access=mmap.ACCESS_READ) as mm:
        chunk = mm[10:20]
        print(chunk == b"0123456789")  # attendu: True

os.remove(path)

utilisation

import mmap
print(hasattr(mmap, "mmap"))

variante(s) utile(s)

import mmap, tempfile, os
with tempfile.NamedTemporaryFile(delete=False) as f:
    f.write(b"abc")
    path = f.name
with open(path, "r+b") as f:
    with mmap.mmap(f.fileno(), 0) as mm:
        mm[0] = ord("A")
print(True)
os.remove(path)

notes

• length=0 mappe tout le fichier; privilégiez un offset/longueur pour très gros.
• Sur Windows, ouvrez en “r+b” pour autoriser le mapping.