occur technicallyby default stdout is just line-buffered when connected to terminalbut it is fully buffered when connected to other devices such as filessocketsand the pipes used here this is why you see script' printed text in shell window immediately as it is producedbut not until the process exits or its buffer fills when its output stream is connected to something else this output buffering is really function of the system libraries used to access pipesnot of the pipes themselves (pipes do queue up output databut they never hide it from readers!in factit appears to occur in this example only because we copy the pipe' information over to sys stdouta built-in file object that uses stream buffering by default howeversuch anomalies can also occur when using other cross-process tools in general termsif your programs engage in two-way dialog like thisthere are variety of ways to avoid buffering-related deadlock problemsflushesas demonstrated in examples - and - manually flushing output pipe streams by calling the file object flush method is an easy way to force buffers to be cleared use sys stdout flush for the output stream used by print argumentsas introduced earlier in this the - python command-line flag turns off full buffering for the sys stdout stream in python programs setting your pythonunbuffered environment variable to nonempty value is equivalent to passing this flag but applies to every program run open modesit' possible to use pipes themselves in unbuffered mode either use low-level os module calls to read and write pipe descriptors directlyor pass buffer size argument of (for unbufferedor (for line-bufferedto os fdopen to disable buffering in the file object used to wrap the descriptor you can use open arguments the same way to control buffering for output to fifo files (described in the next sectionnote that in python xfully unbuffered mode is allowed only for binary mode filesnot text command pipesas mentioned earlier in this you can similarly specify buffering mode arguments for command-line pipes when they are created by os popen and subprocess popenbut this pertains to the caller' end of the pipenot those of the spawned program hence it cannot prevent delayed outputs from the latterbut can be used for text sent to another program' input pipe socketsas we'll see laterthe socket makefile call accepts similar buffering mode argument for sockets (described later in this and book)but in python this call requires buffering for text-mode access and appears to not support linebuffered mode (more on this on toolsfor more complex taskswe can also use higher-level tools that essentially fool program into believing it is connected to terminal these address programs parallel system tools