from alls import a_c ( nameerrorname 'bis not defined load __all__ names only from alls import ab_c_d ab_c_d ( but other importers get every name import alls alls aalls balls _calls _d ( like the _x conventionthe __all__ list has meaning only to the from statement form and does not amount to privacy declarationother import statements can still access all namesas the last two tests show stillmodule writers can use either technique to implement modules that are well behaved when used with from see also the discussion of __all__ lists in package __init__ py files in therethese lists declare submodules to be automatically loaded for from on their container enabling future language features__future__ changes to the language that may potentially break existing code are usually introduced gradually in python they often initially appear as optional extensionswhich are disabled by default to turn on such extensionsuse special import statement of this formfrom __future__ import featurename when used in scriptthis statement must appear as the first executable statement in the file (possibly following docstring or comment)because it enables special compilation of code on per-module basis it' also possible to submit this statement at the interactive prompt to experiment with upcoming language changesthe feature will then be available for the remainder of the interactive session for examplein this book we've seen how to use this statement in python to activate true division in print calls in and absolute imports for packages in prior editions of this book used this statement form to demonstrate generator functionswhich required keyword that was not yet enabled by default (they use featurename of generatorsall of these changes have the potential to break existing code in python xso they were phased in gradually or offered as optional extensionsenabled with this special import at the same timesome are available to allow you to write code that is forward compatible with later releases you may port to someday for list of futurisms you may import and turn on this wayrun dir call on the __future__ module after importing itor see its library manual entry per its documen advanced module topics