the sys module exports additional commonly-used tools that we will meet in the context of larger topics and examples introduced later in this part of the book for instancecommand-line arguments show up as list of strings called sys argv standard streams are available as sys stdinsys stdoutand sys stderr program exit can be forced with sys exit calls since these lead us to bigger topicsthoughwe will cover them in sections of their own introducing the os module as mentionedos is the larger of the two core system modules it contains all of the usual operating-system calls you use in programs and shell scripts its calls deal with directoriesprocessesshell variablesand the like technicallythis module provides posix tools-- portable standard for operating-system calls--along with platformindependent directory processing tools as the nested module os path operationallyos serves as largely portable interface to your computer' system callsscripts written with os and os path can usually be run unchanged on any platform on some platformsos includes extra tools available just for that platform ( low-level process calls on unix)by and largethoughit is as cross-platform as is technically feasible tools in the os module let' take quick look at the basic interfaces in os as previewtable - summarizes some of the most commonly used tools in the os moduleorganized by functional area table - commonly used os module tools tasks tools shell variables os environ running programs os systemos popenos execvos spawnv spawning processes os forkos pipeos waitpidos kill descriptor fileslocks os openos reados write file processing os removeos renameos mkfifoos mkdiros rmdir administrative tools os getcwdos chdiros chmodos getpidos listdiros access portability tools os sepos pathsepos curdiros path splitos path join pathname tools os path exists('path')os path isdir('path')os path getsize('path'if you inspect this module' attributes interactivelyyou get huge list of names that will vary per python releasewill likely vary per platformand isn' incredibly useful system tools