stdin

sys.stdin, sys.stdout, and sys.stderr are file objects corresponding to the interpreter's standard input, output and error streams. stdin is used for all interpreter input except for scripts but including calls to input and rawinput. stdout is used for the output of print and expression statements and for the prompts of [input] and [rawinput]. The interpreter's own prompts and (almost all of) its error messages go to sys.stderr. sys.stdout and sys.stderr needn't be built-in file objects: any object is acceptable as long as it has a write() method that takes a string argument. (Changing these objects doesn't affect the standard I/O streams of processes executed by os.popen, os.system or the exec*() family of functions in the os module.)