namethe notion of importing is also completely general throughout python any file can import tools from any other file for instancethe file py may import py to call its functionbut py might also import py to leverage different tools defined there import chains can go as deep as you likein this examplethe module can import bwhich can import cwhich can import againand so on besides serving as the highest organizational structuremodules (and module packagesdescribed in are also the highest level of code reuse in python coding components in module files makes them useful in your original programand in any other programs you may write later for instanceif after coding the program in figure - we discover that the function spam is general-purpose toolwe can reuse it in completely different programall we have to do is import the file py again from the other program' files standard library modules notice the rightmost portion of figure - some of the modules that your programs will import are provided by python itself and are not files you will code python automatically comes with large collection of utility modules known as the standard library this collectionover modules large at last countcontains platform-independent support for common programming tasksoperating system interfacesobject persistencetext pattern matchingnetwork and internet scriptinggui constructionand much more none of these tools are part of the python language itselfbut you can use them by importing the appropriate modules on any standard python installation because they are standard library modulesyou can also be reasonably sure that they will be available and will work portably on most platforms on which you will run python this book' examples employ few of the standard library' modules--timeitsysand os in last codefor instance--but we'll really only scratch the surface of the libraries story here for complete lookyou should browse the standard python library reference manualavailable either online at python installation (via idle or python' start button menu on some windowsthe pydoc tool discussed in is another way to explore standard library modules because there are so many modulesthis is really the only way to get feel for what tools are available you can also find tutorials on python library tools in commercial books that cover application-level programmingsuch as 'reilly' programming pythonbut the manuals are freeviewable in any web browser (in html format)viewable in other formats ( windows help)and updated each time python is rereleased see for more pointers python program architecture