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