18.2 Enabling Future Language Features

Changes to the language that may potentially break existing code in the future are introduced gradually. Initially, they appear as optional extensions, which are disabled by default. To turn on such extensions, use a special import statement of this form:

from __future__ import featurename

This statement should generally appear at the top of a module file (possibly after a docstring), because it enables special compilation of code on a per-module basis. It's also possible to submit this statement at the interactive prompt to experiment with upcoming language changes; the feature will then be available for the rest of the interactive session.

For example, we had to use this in Chapter 14 to demonstrate generator functions, which require a keyword that is not yet enabled by default (they use a featurename of generators). We also used this statement to activate true division for numbers in Chapter 4.