Master Python’s with Statement: Simplify Resource Management

Have you ever wondered what the with statement does and why we use it? Many Python developers repeatedly see this snippet:

with open('Hi.text', 'w') as f:
    f.write("Hello, there")

Without with, you would need to open the file, write to it, and ensure it is closed using a try … finally block:

f = open('Hi.text', 'w')
try:
    f.write('Hello, there')
finally:
    f.close()

The with keyword shortens this pattern to a single statement, acting as syntactic sugar for the underlying try..finally logic.

In Python, the with statement is a feature of context managers , which provide a reliable way to allocate and release resources.

To create a custom context manager you implement two magic methods: __enter__ and __exit__. For example:

class My_file:
    def __init__(self, fname):
        self.fname = fname

    def __enter__(self):
        self.file = open(self.fname, 'w')
        return self.file

    def __exit__(self, exc_type, exc_val, exc_trace_back):
        if self.file:
            self.file.close()

Using this class:

with My_file('hello.txt') as f:
    f.write('hello, world!')

Behind the scenes, Python calls __init__, then __enter__, runs the block, and finally invokes __exit__. The equivalent explicit calls are:

myfile = My_file('hello.txt')
f = myfile.__enter__()
f.write('hello, world!')
myfile.__exit__(...)

A second approach uses the contextmanager decorator from contextlib:

from contextlib import contextmanager

@contextmanager
def my_file_open(fname):
    try:
        f = open(fname, 'w')
        yield f
    finally:
        print('Closing file')
        f.close()

with my_file_open('hi.txt') as f:
    f.write('hello world')

The contextlib module also provides handy utilities such as closing, which wraps an object and ensures its close method is called, and suppress, which can ignore specified exceptions. For cases where no special cleanup is needed, nullcontext simply returns the object from __enter__ without additional actions. When dealing with asynchronous resources, aclosure (or asynccontextmanager) can be used.

Summary

This article introduced the basic concepts and usage of the with statement and its underlying context manager mechanism, provided class‑based and decorator‑based examples, and pointed to additional tools in contextlib for advanced resource handling.