Utiliser l’instruction with pour les fichiers

Introduction

L’instruction with

# with open('data.txt') as f:
#     content = f.read()
# f is now closed
print('with demo')

Pourquoi with est préférable à try/finally

# Equivalent to:
# f = open('file.txt')
# try:
#     content = f.read()
# finally:
#     f.close()
print('comparison demo')

Plusieurs fichiers

# with open('in.txt') as src, open('out.txt','w') as dst:
#     for line in src:
#         dst.write(line.upper())
print('multi-file demo')

Protocole du gestionnaire de contexte

# f.__enter__() opens
# f.__exit__() closes
print('protocol demo')

Lecture et traitement

lines = ['  hello  \n', '  world  \n']
cleaned = [l.strip() for l in lines if l.strip()]
print(cleaned)

Écriture avec with

# with open('out.txt', 'w') as f:
#     for i in range(10):
#         f.write(f'{i}\n')
print('write with demo')

Vérifier si un fichier existe

import os
print(os.path.exists('/tmp'))
print(os.path.exists('/nonexistent'))

Erreurs de open()

try:
    with open('/nonexistent.txt') as f:
        pass
except FileNotFoundError as e:
    print('File not found:', e)

StringIO pour les fichiers en mémoire

from io import StringIO
buf = StringIO('line1\nline2\n')
for line in buf:
    print(line.rstrip())

Module tempfile

import tempfile
with tempfile.NamedTemporaryFile(mode='w', suffix='.txt', delete=True) as f:
    f.write('temp data')
    print(f.name)

Vérification rapide

Récapitulatif

Poursuivez