[Python-Dev] PEP 318: Let's propose some useful built-in decorators (original) (raw)

Raymond Hettinger python at rcn.com
Sat Apr 3 04:27:52 EST 2004

While I ponder the decorator syntax, let's propose some built-in decorators.

Okay, I'll play (despite my thumbs down on the pep and especially the syntax using a list prefixing the function).

Several people have emphasized that the timing of decorator application is only an implementation detail. So, that leaves open the possibility of using function decorators as compilation pragmas.

One possible pragma tells the compiler that the function may assume that specified global variables are constant and already known. This allows the globals to be loaded in the constant table and accessed with LOAD_GLOBAL instead of LOAD_CONSTANT.

Another pragma tells the compiler to assume that specified attribute lookup targets won't change outside the function. This allows the lookups to be precomputed as soon as the root is available or whenever it changes.

Example

X = 20

[earlybind(int, X), cacheattr("mylist.append", "result.append", "random.random", "self.score")] def meth(self, data) result = [] for sub in data: mylist = [] for elem in sub: if int(elem) == X: mylist.append(elem) else: elem += random.random() self.score(elem) result.append(mylist) return result

Transformation

def meth(self, data, int=int, X=20) _rr = random.random _ss = self.score result = [] _ra = result.append for sub in data: mylist = [] _ma = mylist.append for elem in sub: if int(elem) == X: _ma(elem) else: elem += _rr() _ss(elem) _ra(mylist) return result

Adding the decorator line is sufficient to localize everything in the function, eliminate all lookups from the inner loop, and still keep the code clean and readable.

with-this-much-weirdness-who-needs-to-go-pysco-ly yours,

Raymond Hettinger

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