How deeply does Python Workout: 50 ten-minute exercises cover __enter__ method?

Explains invocation and return-value binding, but stops before custom context-manager implementation details.

enter method

As explained in Python Workout: 50 ten-minute exercises

The __enter__ method is a special Python method invoked when execution enters a context manager and whose return value is bound by the with statement.

When a with statement begins, Python checks the managed object for __enter__ and runs it. The method’s return value becomes the object named after as. For files, __enter__ returns the file object itself, while cleanup happens through __exit__ when the block ends. section 5.10

Track the entry sequence:

Place an object in a with statement. section 5.10
Run __enter__ when the block starts. section 5.10
Bind its return value to the as variable. section 5.10
Run __exit__ when the block ends. section 5.10

File entry in practice

with open('myfile.txt', 'w') as f: f.write('abc\n') f.write('def\n') Here, __enter__ supplies the file object bound to f; __exit__ flushes and closes it after the block. section 5.10

How Python Workout: 50 ten-minute exercises covers it

Cover of Python Workout: 50 ten-minute exercises

liveBook manning.com

Read Python Workout: 50 ten-minute exercises on liveBook Get the book at manning.com

Related concepts

context manager protocolpart of · The context manager protocol is Python’s protocol of __enter__ and __exit__ methods for managing the behavior of a with statement.

This explainer was generated by Manning's knowledge graph from the text of Python Workout: 50 ten-minute exercises. The section links point to the parts of the book it draws on.