How to implement a custom context manager in Python as a function?

In Python, you can create a custom context manager using a function with the @contextlib.contextmanager decorator. This allows you to use the with statement to manage resources.

Here's an example of a simple context manager that prints messages on entry and exit:

from contextlib import contextmanager

@contextmanager
def my_manager():
    print("Entering context")
    try:
        yield  # point where the body of with executes
    finally:
        print("Exiting context")

Usage:

with my_manager():
    print("Inside with block")

Output:

Entering context
Inside with block
Exiting context

Thus, yield splits the code into two parts: before yield is initialization code, after is cleanup code. It's a convenient way to create context managers without writing a class with __enter__ and __exit__ methods.