[Python-Dev] Plea for function/method syntax sugar (PEP 318, with a different syntax) (original) (raw)

Bob Ippolito bob at redivi.com
Wed Feb 18 21:26:33 EST 2004

Some time ago, mwh developed a patch that adds some syntactical sugar
to def, which is equivalent to PEP 318 though it has a different and
more flexible syntax... previous threads can be easily found here:
http://www.google.com/search?q=+site:mail.python.org+%22meth-syntax- sugar%22 the latest version of mwh's patch is here:
http://starship.python.net/crew/mwh/hacks/meth-syntax-sugar-3.diff

Here's a quick overview:

def foo(args) [sugary, expressions, list]: pass

This is equivalent to:

def foo(args): pass foo = list(expressions(sugary(foo)))

This evaluation order is Guido approved, though at least one person
wanted it to be the other way around

One would use this in scenarios such as:

class FooClass(object): def className(klass) [classmethod]: return klass.name

or, even more importantly (to me anyway):

we would change PyObjC to make this a built-in feature.. but, for

completeness: import objc def signature(sig): def _signature(fn): return objc.selector(fn, signature=sig) return _signature

class FooClass(NSObject): def returnsAnInteger(self) [signature('i@:')]: return 1 def returnsVoidTakesAnInteger_(self, anInteger) [signature('v@:i')]: pass

With current syntax, PyObjC is extremely cumbersome:

class FooClass(NSObject): def returnsAnInteger(self): return 1 returnsAnInteger = objc.selector(returnsAnInteger, signature='i@:')

 def returnsVoidTakesAnInteger_(self, anInteger):
     pass
 returnsVoidTakesAnInteger_ =

objc.selector(returnsVoidTakesAnInteger_, signature='v@:i') # these are actually short examples, compare to something like: # textView_completions_forPartialWordRange_indexOfSelectedItem_

Why we need this: Without it, it's hard use PyObjC correctly. ObjC selector
nomenclature is extremely verbose, and your fingers hurt after a while
having to type each function name three times. The function name
is important, because the objc.selector type has to convert it to a
selector:that:uses:colons:, or else the colon:using:name: would have to
be specified manually. It makes classmethod/staticmethod/etc more palatable.

What the patch doesn't do: lambda is not allowed in the "sugary expressions list" there's no *expansion and it won't take an actual list so if you want
a prebaked list of transformations then you'll have to roll a callable
that does it such as:

def prebake(*expressions): def _prebake(fn): for transformation in expressions: fn = transformation(fn) return fn return fn

This syntactical sugar for def is so unbelievably important to PyObjC
(and likely other projects) that I am willing to distribute my own
modified version of Python if it doesn't make 2.4 (though I would
probably use Stackless as the base, but that's another plea for another
day).

The patch looks like it still applies to CVS HEAD, but there is a
little fuzz on hunk 2. I have not tested it yet, but I have tested it
against CVS HEAD of the 2.3.3 based Stackless.

I'm willing to help however I can in order to get this into Python 2.4.

-bob

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