What is the python keyword "with" used for?

python

context-managers

resource-management

best-practices

byAlex Kataev·Oct 10, 2024

The with statement in Python is a context manager that simplifies the process of managing setup and cleanup actions. Notably, it is widely used in handling resources like files and network connections, ensuring they are properly dealt with, even when exceptions occur.

with open('example.txt') as file:  # Opens file
    contents = file.read() # Reads contents
# No explicit close! The file says "Goodbye 👋" and closes itself here.

Dive deeper into "with" and context managers

The with keyword in Python introduces a context manager. This powerful tool ensures efficient resource management, offering a robust mechanism for setup and cleanup stages. Let me show you the magic:

Simplified resource management

No need for explicit try/finally blocks when you use the with statement:

Before embracing "with":

file = open('example.txt', 'r')  # Opens an ancient scroll
try:
    contents = file.read()  # Reads the secrets inside
finally:
    file.close()  # Closes the scroll
# Oh no, the scroll was left open and ancient wisdom spilled out! 😱

After adopting "with":

with open('example.txt', 'r') as file:  # Opens the scroll
    contents = file.read()  # Reads the wisdom
# The scroll's secrets are safe and sound. 😌

The latter approach is cleaner, safer, and less error-prone.

Graceful exception handling

The with statement not only helps manage resources but also handles exceptions within its block, ensuring resources are properly released.

DIY context managers

You can mould your own context managers by defining classes with __enter__ and __exit__ methods:

class ManagedResource:  # Assemble your transformer bot
    def __enter__(self):  # Transform into "resource" mode
        return self
    def __exit__(self, exc_type, exc_value, traceback):  # Transform back to "idle" mode
        pass

with ManagedResource() as resource:  # Calling the transformer bot
    pass  # to do some heavy lifting

Many built-in Python libraries already provide context managers for their resources, ready for use with the with keyword.

Deeper dive: Using "with" beyond file operations

Aside from files, there are other instances where with is your go-to keyword:

Database transactions: Can be committed or rolled back, ensuring smooth operations.
Thread locks in Python's threading library: Can be acquired and released, ensuring event sequence.
Temporary changes to system attributes or class properties: Can be made and undone, ensuring system state consistency.

The nitty-gritty of "with"

Advanced resource allocation and cleanup

By employing the with statement, you can:

Stack multiple context managers with a single with statement:

with open('input.txt') as infile, open('output.txt', 'w') as outfile:  # Two files, one motive
    outfile.write(infile.read())  # No more chasing down resource leaks 🕵️‍♀️