[natch]

IMHO, sadly, that part is serving as a shibboleth.

The clue is how he explains all the simple parts of the script with comments, but leaves this part unexplained, making some of us feel left out of the cool club. Implying: if you don't grasp it immediately you must not be up to it.

Overall it's a great post, but as to the cryptic parts of it, it's disappointing to see this kind of thing on the part of someone we all look up to. It would be more generous of spirit if he were to have written this in a readable, self explanatory way, like the rest of the code... as python should be written.

Sigh. Norvig has a posse, but I thought it had to be said.

    >>> import this
   ...
   "Readability matters"
   ...
   "Sparse is better than dense"
   ...
   "If the implementation is hard to explain, it's a bad idea"

[magicalist]

First, it is explained in the text above it.

Second, seriously?

A line of code that isn't as clear as it could be in an ipython notebook he probably dashed off in an hour is somehow a reflection on his generosity of spirit? I think you need to recheck your expectations.

[dded]

> First, it is explained in the text above it.

A minor correction: the explanation for this heuristic was added later. (I first opened this in a tab, and then didn't read the tab till much later. I also wondered about the heuristic and didn't think to hit reload till I saw your reply.)

But you're right, there is certainly nothing ungenerous from Norvig here. Quite the opposite.