Kontekst menejerlar (context managers)

Kontekst menejer (context manager) — resurslarni ishonchli boshqarish uchun ishlatiladigan Python imkoniyati. U fayl, tarmoq ulanishi yoki ma'lumotlar bazasi ulanishi kabi resurslar to'g'ri ochilib-yopilishini kafolatlaydi, hatto jarayon o'rtasida xato bo'lsa ham.

Siz ham fayl ochib, keyin yopishni unutganmisiz? Python'da buni with kalit so'zi bilan oson oldini olish mumkin.

1. with kalit so'zi

Kontekst menejerdan foydalanishning eng keng tarqalgan usuli — with buyrug'i.

Kontekst menejersiz (resurs yopilmay qolishi mumkin):

file = open("data.txt", "w")
try:
    file.write("Hello World")
finally:
    file.close() # Uni qo'lda yopishimiz shart

Kontekst menejer bilan (xavfsiz va toza):

with open("data.txt", "w") as file:
    file.write("Hello World")

# Fayl bu yerda avtomatik yopiladi, hatto yozish paytida xato bo'lsa ham.

2. O'zingiz kontekst menejer yaratish

O'zingizning kontekst menejeringizni __enter__ va __exit__ metodlariga ega sinf orqali yaratishingiz mumkin.

__enter__: with blokiga kirilganda ishlaydi. Qaytgan qiymat as ... dagi o'zgaruvchiga beriladi. __exit__: with blokidan chiqilganda ishlaydi (normal tugash yoki xato).

Misol: ma'lumotlar bazasi ulanish menejeri (simulyatsiya)

class ManageDB:
    def __init__(self, db_name):
        self.db_name = db_name

    def __enter__(self):
        print(f"--> Opening connection to {self.db_name}")
        return self # Bu obyekt 'db' o'zgaruvchisiga aylanadi

    def query(self, sql):
        print(f"Executing query: {sql}")

    def __exit__(self, exc_type, exc_value, traceback):
        print(f"<-- Closing connection to {self.db_name}")
        # Xato bo'lsa, exc_type None bo'lmaydi
        if exc_type:
            print(f"Xato yuz berdi: {exc_value}")
        # Xatoni bostirishni xohlasangiz True qaytaring (dastur buzilmaydi)
        # Xato ko'tarilishini xohlasangiz False qaytaring (standart)

# Foydalanish
with ManageDB("users_db") as db:
    db.query("SELECT * FROM users")
    
# Natija:
# --> Opening connection to users_db
# Executing query: SELECT * FROM users
# <-- Closing connection to users_db

3. contextlib dan foydalanish

Python contextlib modulini beradi. U generator va @contextmanager dekoratori yordamida kontekst menejer yaratishni osonlashtiradi. Bu sinf yaratishdan ixchamroq.

from contextlib import contextmanager

@contextmanager
def open_my_file(name):
    try:
        print("Opening file...")
        f = open(name, "w")
        yield f
    finally:
        print("Closing file...")
        f.close()

# Foydalanish
with open_my_file("test.txt") as f:
    f.write("Test 123")

yielddan oldingi kod __enter__, finally blokidagi kod esa __exit__.

4. Amaliy misol: bajarilish vaqtini o'lchash

Kod bloki qancha vaqt ishlaganini o'lchash uchun kontekst menejer yozish mumkin.

import time
from contextlib import contextmanager

@contextmanager
def timer():
    start = time.time()
    yield
    end = time.time()
    print(f"Execution time: {end - start:.4f} seconds")

with timer():
    # Og'ir jarayonni simulyatsiya qilish
    time.sleep(1)
    x = sum(range(1000000))

# Natija: Execution time: 1.0xxx seconds

5. Bir vaqtning o'zida bir nechta resursni boshqarish

Bitta with operatori vergul bilan ajratilgan bir nechta kontekst menejerni boshqarishi mumkin. Har biri chapdan o'ngga ishga tushiriladi va teskari tartibda yopiladi:

with open("a.txt", "w") as a, open("b.txt", "w") as b:
    a.write("file A")
    b.write("file B")
# ikkala fayl ham bu yerda yopiladi

Uzun ro'yxatlar uchun ularni qavslarga olib, qatorlarga bo'ling:

with (
    open("a.txt", "w") as a,
    open("b.txt", "w") as b,
):
    a.write("A")
    b.write("B")

6. contextlib.suppress bilan xatolarni bostirish

Muayyan xatoni rostdan ham e'tiborsiz qoldirmoqchi bo'lsangiz, contextlib.suppress bo'sh try/except'dan tozaroq:

import os
from contextlib import suppress

# Fayl mavjud bo'lsa o'chiramiz, bo'lmasa e'tiborsiz qoldiramiz
with suppress(FileNotFoundError):
    os.remove("maybe_missing.txt")

print("Continued without crashing")

Xulosa

• Fayl yoki ulanish bilan ishlaganda imkon qadar with ishlating.
• __enter__ va __exit__ bilan o'zingiz resurs boshqaruvini yarating.
• Funksional va ixcham usul uchun @contextmanager dan foydalaning.
• Bir nechta kontekst menejerni bitta with'da birlashtiring va kutilgan xatolarni e'tiborsiz qoldirish uchun suppress ishlating.