Possible errors in Chapter 15, element_generic example about deadsimplepython HOT 1 CLOSED

Hi Kirill!

I'll start with (2), as you are absolutely right. While @typing.overload should work as I describe normally, it doesn't play well with other decorators. That was a major oversight on my part. Thankfully, my publisher is reprinting the book, so we'll get that fixed.

As to (1), you're definitely correct that if 1 in formula.keys(): fails. That should have checked for H instead. Not sure how I overlooked that obvious detail.

As to the concern about the possible brittleness of using __hash__() like this, I'm not terribly concerned. I did write the classes to depend on that implementation detail, so the element symbol (guaranteed unique for all real elements entered correctly) is used as the unique identifier. You're correct that it tightly couples Element and Compound, but that's one of those acceptable little compromises to make a sane example. In fact, this is one of my least favorite examples in the book...it took me three weeks to develop, and I was fairly going out of my mind by time I finished it. On the upside, it shows how hashes are used, and that makes the compromise a bit valuable in itself.

Thanks for your comments!

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