variablebut not very permanent one changes to sys path are retained only until the python process endsand they must be remade every time you start new python program or session howeversome types of programs ( scripts that run on web servermay not be able to depend on pythonpath settingssuch scripts can instead configure sys path on startup to include all the directories from which they will need to import modules for more concrete use casesee example - in the prior -there we had to tweak the search path dynamically this waybecause the web server violated our import path assumptions windows directory paths notice the use of raw string literal in the sys path configuration codebecause backslashes normally introduce escape code sequences in python stringswindows users should be sure to either double up on backslashes when using them in dos directory path strings ( in " :\\dir"\is an escape sequence that really means \)or use raw string constants to retain backslashes literally ( " :\dir"if you inspect directory paths on windows (as in the sys path interaction listing)python prints double \to mean single technicallyyou can get away with single in string if it is followed by character python does not recognize as the rest of an escape sequencebut doubles and raw strings are usually easier than memorizing escape code tables also note that most python library calls accept either forward (/or backward (\slashes as directory path separatorsregardless of the underlying platform that isusually works on windows too and aids in making scripts portable to unix tools in the os and os path modulesdescribed later in this further aid in script path portability the loaded modules table the sys module also contains hooks into the interpretersys modulesfor exampleis dictionary containing one name:module entry for every module imported in your python session or program (reallyin the calling python process)sys modules {'reprlib'more deleted list(sys modules keys()['reprlib''heapq''__future__''sre_compile''_collections''locale''_sre''functools''encodings''site''operator''io''__main__'more deleted sys sys modules['sys' system tools