81. Context Managers with contextlib

Here are 10 Python code snippets demonstrating how to use the contextlib module to create reusable context managers.

1. Using contextlib.contextmanager for Simple Context Managers

This example shows how to create a simple context manager using the @contextmanager decorator.

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from contextlib import contextmanager

@contextmanager
def simple_context():
    print("Entering the context")
    yield
    print("Exiting the context")

# Using the context manager
with simple_context():
    print("Inside the context")

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2. Managing File Resources with contextlib.closing

The closing context manager is useful for closing resources like network connections or file handles that don't support the with statement natively.

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from contextlib import closing
import urllib.request

with closing(urllib.request.urlopen('http://example.com')) as page:
    content = page.read()
    print(content[:100])  # Print the first 100 characters of the page

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3. Suppressing Exceptions Using contextlib.suppress

The suppress context manager is used to suppress specified exceptions during execution.

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from contextlib import suppress

with suppress(FileNotFoundError):
    # If the file doesn't exist, it will be suppressed
    open('non_existing_file.txt', 'r')

print("Program continued without exception.")

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4. Timing a Code Block Using a Context Manager

Creating a custom context manager to measure the execution time of a block of code.

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import time
from contextlib import contextmanager

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

# Using the timer context manager
with timer():
    time.sleep(1)  # Simulate a delay

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5. Custom Context Manager Using a Class

Implementing a custom context manager using a class with __enter__ and __exit__ methods.

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class MyContextManager:
    def __enter__(self):
        print("Entering context")
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        print("Exiting context")

# Using the context manager
with MyContextManager():
    print("Inside the context")

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6. Using contextlib.nested for Multiple Contexts

The nested function (deprecated in Python 3.1, replaced by with statements in with statements) allows managing multiple contexts simultaneously.

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from contextlib import nested

with nested(open('file1.txt', 'r'), open('file2.txt', 'r')) as (f1, f2):
    print(f1.read())
    print(f2.read())

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7. Using contextlib.ExitStack to Handle Multiple Context Managers Dynamically

ExitStack can be used for handling a dynamic number of context managers.

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from contextlib import ExitStack

with ExitStack() as stack:
    file1 = stack.enter_context(open('file1.txt', 'r'))
    file2 = stack.enter_context(open('file2.txt', 'r'))
    print(file1.read())
    print(file2.read())

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8. Redirecting Standard Output Using contextlib.redirect_stdout

Redirecting standard output to a file or other stream using redirect_stdout.

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from contextlib import redirect_stdout

with open('output.txt', 'w') as f:
    with redirect_stdout(f):
        print("This will be written to the file.")

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9. Creating a Context Manager for Database Connections

A context manager for handling database connections.

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import sqlite3
from contextlib import contextmanager

@contextmanager
def open_db(db_name):
    conn = sqlite3.connect(db_name)
    try:
        yield conn
    finally:
        conn.close()

# Using the database connection context manager
with open_db('my_database.db') as db:
    cursor = db.cursor()
    cursor.execute('SELECT * FROM my_table')
    print(cursor.fetchall())

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10. Handling Temporary Directory Creation Using TemporaryContext

Creating and cleaning up a temporary directory with a context manager.

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import tempfile
import os
from contextlib import contextmanager

@contextmanager
def temporary_directory():
    temp_dir = tempfile.mkdtemp()
    try:
        yield temp_dir
    finally:
        os.rmdir(temp_dir)

# Using the temporary directory context manager
with temporary_directory() as temp_dir:
    print(f"Temporary directory created: {temp_dir}")

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