Hacker News Reader

Comment by jason_s | Hacker News Reader

I hate the new @ operator for matrix multiplication, it just looks ugly. (And I use numpy matrix math all the time.) But whatever.

View on HN

As a fellow numpy user - why? I would love having sugar for this, I use it all the time. Introducing a single operator to overload seems odd but it's definitely a pragmatic solution to making code more readable. What would you do instead?

Personally, I'd have made it a diglyph of some sort, like :* or ^*, to make it obvious to someone looking at python math code for the first time that this is a multiplication operator. @ just leaves a weird taste here.

Agreed; this needs an operator, but it doesn't need a single-character operator, and the operator should have had * in it.

The pros and cons of different operator possibilities are discussed extensively in the PEP that added the matrix multiplication operator.

Direct link: http://legacy.python.org/dev/peps/pep-0465/#choice-of-operat...

I love the snark in that PEP:

> APL apparently used +.× , which by combining a multi-character token, confusing attribute-access-like . syntax, and a unicode character, ranks somewhere below U+2603 SNOWMAN on our candidate list.

and then later, one of the reasons @ is better than the alternatives:

> Whatever, we have to pick something.

What about the & char?

& is the bitwise and operator.

Yep, forgot thanks.

Not particularly well, though. No actual explanation was given for rejecting ^(star), and :(star) wasn't even mentioned.

(Aside: HN really needs a better way to escape star inline in text.)

It sounded like there was a bit of general preference for a single-character operator, which is a sentiment I can get behind.

OCaml has * for int multiplication and * . for float multiplication. you cannot overload but you can define your own, so people tend to do things like define *: for complex multiplication.

In R %*% is matrix multiplication.

Python 3.5: In which your email address became syntactically correct.

What alternative would you propose?

Given that having an operator for this was deemed important for more readable numeric code, and that * was already taken, there weren't too many fabulous choices left.

https://www.python.org/dev/peps/pep-0465/#choice-of-operator

Also it feels like wasting a character on something that only a small number of users are likely going to need.

Not necessarily. You can overload @ to do some other kind of object combination, which fits your paradigm better. You're not tied to using it for matrix multiplication.

Reply on news.ycombinator.com