On 2/11/2020 10:58 AM, Brandt Bucher wrote:

I have just pushed the first draft of PEP 614:

https://www.python.org/dev/peps/pep-0614/

It proposes that the current decorator syntax restrictions be relaxed to allow any valid expression. Please let me know what you think!

I think it should start with a description of the current expression restrictions. It assumes the reader is familiar with them. Other than that, it seems okay to me. Eric

there are no known examples of binary matrix multiplication results which may used as decorators.

This is misleading. There are multiple libraries on PyPI that wrap up functions to add additional operators and methods including @ for compose. (It’s also been proposed and rejected repeatedly for the builtin type, going back to the rejected PEPs in 2000 that originally proposed a matmul operator.) And composing two decorators isn’t binary matrix multiplication, but it is a use of the @ operator; and it gives you results which could be used as decorators. For example, if I have a logcall decorator that wraps its function with calls to logging.log that show when the function is entered and exited, and a daytime decorator that skips the function call if it’s nighttime, then logcall@daytime is a decorator which skips the function call if it’s nighttime but always logs either way, while daytime@logcall skips both. I don’t think that this is a practical problem. I don’t know how often people use these libraries to compose decorators, but even if it’s very frequent (which it probably isn’t), it wouldn’t look at all ambiguous to a human to mix with this feature, because the following end up meaning the same thing: @daytime@logcall def cheese(…): @daytime @logcall def cheese(…): Try it with composing decorators that take arguments and return the actual decorator, etc.; it’s never ambiguous or misleading to the reader. So, I think the PEP can dismiss the problem, just not in the way it currently does.

I think it should start with a description of the current expression restrictions.

I agree that this would be a good addition. Thanks!

This github search seems to return more direct hits of this usage pattern: https://github.com/search?l=Python&q=__matmul__+curry&type=Code On Tue, Feb 11, 2020 at 11:38 AM Nathan wrote:

It doesn't look like it's popular or used much, but i spent a minute or two looking via github search and found this library that uses @ for currying:

https://github.com/kanales/spycy/blob/master/spycy/__init__.py#L87

On Tue, Feb 11, 2020 at 11:26 AM Brandt Bucher wrote:

...

Thanks for bringing this up; I didn't know that there were any libraries using @ like this.

I've spent some time searching on Google, PyPI, and GitHub, though, and I can't find anything that advertise this functionality. Do you have the names of any of them handy, so I could perhaps add a simple, real-world example of the newly valid usage?

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i spent a minute or two looking via github search and found this library that uses @ for currying...

fn-compose looks like the right thing...

Hm, exploring these a bit more, both libraries are unstable, haven't been updated in several years, and have no watchers, stars, or dependents on GitHub. I think it would be inappropriate to use either of these as a "real world" example, but I still am considering rewording the section to acknowledge that this design pattern does seems to exist in some form.

Honestly I don't see why the PEP even needs to bring up the matrix multiply operator.

I was on the fence when writing this draft anyways. Given that the feedback ranges from "this problem should be dismissed differently" to "this isn't a problem", I think I'll just go ahead and drop it. :)