`contextlib`

The Python contextlib module provides utilities for working with context managers, which allows you to allocate and release resources precisely.

This module is especially useful for creating context managers and managing resources in a clean and safe way.

Here’s a quick toy example:

Python
      
        
      
    
>>> from contextlib import contextmanager

>>> @contextmanager
... def context():
...     print("Entering")
...     yield
...     print("Exiting")
...

>>> with context():
...     print("Inside")
...
Entering
Inside
Exiting

Key Features

Provides utilities for creating context managers
Facilitates resource management and cleanup
Offers decorators and helper functions for common context manager patterns
Supports context manager chaining and nesting

Frequently Used Classes and Functions

Object	Type	Description
`contextlib.contextmanager`	Decorator	Converts a generator function into a context manager
`contextlib.closing`	Class	Ensures that a resource is closed when done
`contextlib.suppress`	Class	Suppresses specified exceptions
`contextlib.ExitStack`	Class	Allows dynamic management of a stack of context managers

Examples

Using @contextmanager to create a function-based context manager:

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>>> from contextlib import contextmanager

>>> @contextmanager
... def writable_file():
...     try:
...         print("Open file for writing...")
...         file = open("hello.txt", mode="w", encoding="utf-8")
...         yield file
...     finally:
...         print("Closing file...")
...         file.close()
...

>>> with writable_file() as file:
...     file.write("Hello, World!")
...
Open file for writing...
13
Closing file...

Note: Using open() is preferred for files. The example above is for demonstration purposes only.

Automatically closing a file using the closing() context manager:

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>>> from contextlib import closing
>>> from urllib.request import urlopen

>>> with closing(urlopen("http://www.example.com")) as page:
...     for line in page:
...         print(line)
...

Suppressing specific exceptions with the suppress() context manager:

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>>> from contextlib import suppress

>>> with suppress(FileNotFoundError):
...     open("non_existent_file.txt")
...

Common Use Cases

Creating lightweight context managers without defining a full class
Managing multiple context managers dynamically
Ensuring resources are properly cleaned up, such as file handles or network connections
Suppressing specific exceptions in a clean and controlled manner

Real-World Example

Suppose you want to handle multiple resources that need to be opened and closed. Using ExitStack, you can manage these resources efficiently:

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>>> from contextlib import ExitStack
>>> files = ["file1.txt", "file2.txt"]

>>> with ExitStack() as stack:
...     file_objects = [
...         stack.enter_context(open(fname, "w")) for fname in files
...     ]
...     for file in file_objects:
...         file.write("Hello, World!")
...
13
13

In this example, ExitStack allows you to enter and manage multiple context managers, ensuring that they’re all properly closed when the block is exited. This approach facilitates resource management when dealing with multiple context managers.

Tutorial

Context Managers and Python's with Statement

In this step-by-step tutorial, you'll learn what the Python with statement is and how to use it with existing context managers. You'll also learn how to create your own context managers.

intermediate python

For additional information on related topics, take a look at the following resources: