Dmi Baranov added the comment: I found a little difference in isatty implementaions: Windows Determines whether a file descriptor is associated with a character device [1] Unix Test whether a file descriptor refers to a terminal [2] So, we having a same behavior for pipes, but different for I/O redirection with pseudo-character devices: $ ./python -c "import os;print(os.isatty(0))" < /dev/null False e:\PCbuild>python_d.exe -c "import os;print(os.isatty(0))" < NUL True Other pseudo devices works simular: e:\PCbuild>python_d.exe -c "import os;print(os.isatty(0))" < CON True I having a snippet to fix that, should I open a new issue for patch? [1] http://msdn.microsoft.com/en-us/library/f4s0ddew.aspx [2] http://man7.org/linux/man-pages/man3/isatty.3.html ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue18553> _______________________________________