Instrukcja with w pracy z plikami

Wprowadzenie

Instrukcja with

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

Dlaczego with jest lepsze niż try/finally

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

Wiele plików

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

Protokół menedżera kontekstu

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

Odczyt i przetwarzanie

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

Zapisywanie za pomocą with

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

Sprawdzanie, czy plik istnieje

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

Błędy open()

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

StringIO dla plików w pamięci

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

Moduł tempfile

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

Szybkie sprawdzenie

Podsumowanie

Kontynuuj naukę