Python Interactive Interpreter always returns “Invalid syntax” on Windows

Question

I\'ve encountered an extremely confusing problem. Whatever I type into the Python interpreter returns \"Invalid Syntax\". See examples below. I\'ve tried fooling around w

Answer 1

There is a known problem when running Python interactively and unbuffered, which is scheduled for fixing in 3.2 - and may be backported to older versions, see http://bugs.python.org/issue11098

The nasty thing is, one may be using unbuffered I/O without realising it. In my case (Python 2.5.4 (r254:67916)), I had some time ago set an environment variable such that Python would always run unbuffered (on Windows, this is PYTHONUNBUFFERED=YES, or whatever non-empty string substituted for YES) and then forgot about it. Removing the env.var. solved the problem for me.

So it may be worthwhile checking for this environment variable. It's not set by default.