What is the python “with” statement designed for?

Question

I came across the Python with statement for the first time today. I\'ve been using Python lightly for several months and didn\'t even know of its existence! G

Answer 1

The Python with statement is built-in language support of the Resource Acquisition Is Initialization idiom commonly used in C++. It is intended to allow safe acquisition and release of operating system resources.

The with statement creates resources within a scope/block. You write your code using the resources within the block. When the block exits the resources are cleanly released regardless of the outcome of the code in the block (that is whether the block exits normally or because of an exception).

Many resources in the Python library that obey the protocol required by the with statement and so can used with it out-of-the-box. However anyone can make resources that can be used in a with statement by implementing the well documented protocol: PEP 0343

Use it whenever you acquire resources in your application that must be explicitly relinquished such as files, network connections, locks and the like.