[Python-Dev] Pep 318 - new syntax for wrappers (original) (raw)

Bob Ippolito bob at redivi.com
Wed Mar 3 13:55:08 EST 2004

On Mar 3, 2004, at 10:20 AM, Jewett, Jim J wrote:

I think everyone agrees that decorators are useful, and the current idiom is awkward; the only real argument is over how to improve it. Proponents want something easy to type; others want something explicit.

(1) Eventually, there will be another good idea. Therefore, we should define a general extension syntax, rather than a special case for this particular extension. def func(args) [wrapper1, wrapper2]: uses up the syntax forever.

I agree with Skip on this one, ANYTHING that transforms a function in ANY way can be represented by this decorator syntax.

The only thing we can't change is the fact that Python will compile the code block once before we get ahold of it, and we have no control over the Python compiler/grammar while it is being compiled. These might be more relevant for something like PyPy though, but there's nothing that would really stop you from throwing keywords inside the [wrapper] block if you need to let the compiler know about something if/when that ever happens.

(2) Wrappers are not essential to understanding functions, and should not pretend to be.

They are not essential to understanding how to make your own functions or methods, but they are essential to understanding other people's code that uses them:

def foo(args) [classmethod]:
    pass

is quite different than what would happen otherwise. The default behavior of code and class blocks is fine for most people, but once you start doing a lot of metamagic and turn python into a domain specific language, they become very relevant.

In most languages, classifiers are always relevant. Defaults might save you from writing "int", "public", or "synchronized", but the classification still happens. If you want your code to be robust, you need to at least understand the possible classifiers, and when to use them. This means you need to learn something about each of them soon after "Hello World".

In python, these extensions really are optional. The syntax should make it clear that newbies can ignore the whole construction, and do not need to know any specific wrappers. def func(args) [wrapper1, wrapper2]: suggests that the extensions are part of basic function syntax. Lack of documentation for wrapper1 and wrapper2 (which may not be part of the core language) presents an extra barrier. So does the fact that this is a new meaning for [], at least under the current patch. People can learn to ignore it -- but only if they have already committed to python. Each new barrier to entry makes a newbie more likely to give up before starting.

Since when do newbies read the "language lawyer" documentation? They read the tutorials and existing code. No tutorials or existing code (on top of the regular python compiler) use this syntax yet, so newbies are obviously not going to see it.

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