Kontekst menejerlar (context managers)

Context manager - resurslarni boshqarish uchun juda chiroyli Python imkoniyati. Ular fayl, network connection yoki database connection 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

Context manager ishlatishning eng keng tarqalgan usuli - with statement.

Context manager'siz (leak xavfi):

file = open("data.txt", "w")
try:
    file.write("Hello World")
finally:
    file.close() # We must manually close it

Context manager 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 context manager yaratish

O'zingizning context manager'ingizni __enter__ va __exit__ metodlariga ega class orqali yaratishingiz mumkin.

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

Misol: database connection manager (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 # This object becomes 'db' variable

    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 decorator yordamida context manager yaratishni osonlashtiradi. Bu class 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 context manager 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

Xulosa

• Fayl yoki connection bilan ishlaganda imkon qadar with ishlating.
• __enter__ va __exit__ bilan o'zingiz resurs boshqaruvini yarating.
• Funksional va ixcham usul uchun @contextmanager dan foydalaning.