This is a good explanation, but I still prefer the one from StackOverflow:

    http://stackoverflow.com/questions/231767/the-python-yield-keyword-explained?answertab=votes#tab-top

You can tell it's popular, because it's been submitted to many times:

https://news.ycombinator.com/item?id=1603179

https://news.ycombinator.com/item?id=3066144

https://news.ycombinator.com/item?id=4769449

https://news.ycombinator.com/item?id=4810661

https://news.ycombinator.com/item?id=5124929 - Good discussion

https://news.ycombinator.com/item?id=5399772