the arguments to os execlp specify the program to be run by giving command-line arguments used to start the program ( what python scripts know as sys argvif successfulthe new program begins running and the call to os execlp itself never returns (since the original program has been replacedthere' really nothing to return toif the call does returnan error has occurredso we code an assert after it that will always raise an exception if reached there are handful of os exec variants in the python standard librarysome allow us to configure environment variables for the new programpass command-line arguments in different formsand so on all are available on both unix and windowsand they replace the calling program ( the python interpreterexec comes in eight flavorswhich can be bit confusing unless you generalizeos execv(programcommandlinesequencethe basic "vexec form is passed an executable program' namealong with list or tuple of command-line argument strings used to run the executable (that isthe words you would normally type in shell to start programos execl(programcmdarg cmdarg cmdargnthe basic "lexec form is passed an executable' namefollowed by one or more command-line arguments passed as individual function arguments this is the same as os execv(program(cmdarg cmdarg )os execlp os execvp adding the letter to the execv and execl names means that python will locate the executable' directory using your system search-path setting ( pathos execle os execve adding letter to the execv and execl names means an extralast argument is dictionary containing shell environment variables to send to the program os execvpe os execlpe adding the letters and to the basic exec names means to use the search path and to accept shell environment settings dictionary so when the script in example - calls os execlpindividually passed parameters specify command line for the program to be run onand the word python maps to an executable file according to the underlying system search-path setting environment variable (pathit' as if we were running command of the form python child py in shellbut with different command-line argument on the end each time forking processes