sys.stderr

sys.stderr

File objects used by the interpreter for standard input, output and errors:

• stdin is used for all interactive input (including calls to input());
• stdout is used for the output of print() and expression statements and for the prompts of input();
• The interpreter’s own prompts and its error messages go to stderr.

These streams are regular text files like those returned by the open() function. Their parameters are chosen as follows:

• The character encoding is platform-dependent. Under Windows, if the stream is interactive (that is, if its isatty() method returns True), the console codepage is used, otherwise the ANSI code page. Under other platforms, the locale encoding is used (see locale.getpreferredencoding()).

  Under all platforms though, you can override this value by setting the PYTHONIOENCODING environment variable before starting Python.

• When interactive, standard streams are line-buffered. Otherwise, they are block-buffered like regular text files. You can override this value with the -u command-line option.