CORRECTION: My regret was referring to a problem where this code worked in Python 2 but not Python 3: x = 100 y = [x+i for i in range(2)] In Python 3

CORRECTION: My regret was referring to a problem where this code worked in Python 2 but not Python 3: x = 100 y = [x+i for i in range(2)] In Python 3 I kept seeing NameError: name 'x' is not defined However, after working around this problem with fixes like this - x = 100 y = (lambda x=x: [x+i for i in range(2)])() I have just discovered that the different scope treatment was due to a problem with IPython when using it in embed mode, for example by calling it with the following command: $ python -c "import IPython;IPython.embed()" It goes away when you call ipython directly $ ipython I mistakenly attributed this problem to Python 3 for years, I guess I introduced the problem because I had a different way of invoking Python 2 and Python 3 - yeesh.