operating system services unlink(pathremoves the file path same as remove(utime(path(atimemtime)sets the access and modified time of the file to the given values (the second argument is tuple of two items the time arguments are specified in terms of the numbers returned by the time time(function walk(top [topdown [onerror [,followlinks]]]creates generator object that walks through directory tree top specifies the top of the directoryand topdown is boolean that indicates whether to traverse directories in top-down (the defaultor bottom-up order the returned generator produces tuples (dirpathdirnamesfilenameswhere dirpath is string containing the path to the directorydirnames is list of all subdirectories in dirpathand filenames is list of the files in dirpathnot including directories the onerror parameter is function accepting single argument if any errors occur during processingthis function will be called with an instance of os error the default behavior is to ignore errors if directory is walked in top-down mannermodifications to dirnames will affect the walking process for exampleif directories are removed from dirnamesthose directories will be skipped by defaultsymbolic links are not followed unless the followlinks argument is set to true process management the following functions and variables are used to createdestroyand manage processesabort(generates sigabrt signal that' sent to the calling process unless the signal is caught with signal handlerthe default is for the process to terminate with an error defpath this variable contains the default search path used by the exec* *(functions if the environment doesn' have 'pathvariable execl(patharg arg equivalent to execv(path(arg arg )execle(patharg arg envequivalent to execve(path(arg arg )envexeclp(patharg arg equivalent to execvp(path(arg arg )execv(pathargsexecutes the program path with the argument list argsreplacing the current process (that isthe python interpreterthe argument list may be tuple or list of strings lib fl ff