operating system services he modules in this provide access to wide variety of operating system services with an emphasis on low-level /oprocess managementand the operating environment modules that are commonly used in conjunction with writing systems programs are also included--for examplemodules to read configuration fileswrite log filesand so forth "file and directory handling,covers high-level modules related to file and filesystem manipulation--the material presented here tends be at lower level than that most of python' operating system modules are based on posix interfaces posix is standard that defines core set of operating system interfaces most unix systems support posixand other platforms such as windows support large portions of the interface throughout this functions and modules that only apply to specific platform are noted as such unix systems include both linux and mac os windows systems include all versions of windows unless otherwise noted readers may want to supplement the material presented here with additional references the programming languagesecond edition by brian kernighan and dennis ritchie (prentice hall provides good overview of filesfile descriptorsand the low-level interfaces on which many of the modules in this section are based more advanced readers may want to consult book such as advanced programming in the unix environment nd edition by richard stevens and stephen rago (addison wesley for an overview of general conceptsyou may want to locate college textbook on operating systems howevergiven the high cost and limited day-to-day practical utility of these booksyou're probably better off asking nearby computer science student to loan you their copy for weekend commands the commands module is used to execute simple system commands specified as string and return their output as string it only works on unix systems the functionality provided by this module is somewhat similar to using backquotes (`in unix shell script for exampletyping commands getoutput('ls - 'is similar to saying =`ls -lgetoutput(cmdexecutes cmd in shell and returns string containing both the standard output and standard error streams of the command lib fl ff