On 27.10.15 19:45, Serhiy Storchaka wrote:
There is known trick to optimize a function:
def foo(x, y=0, len=len, pack=struct.pack, maxsize=1<<BPF): ...
It has a side effect: change function's signature. Would be nice to have a way to set function's local variables at creation time without affecting a signature.
Possible syntax (I'm not sure what is better):
1. Similar to "global" and "nonlocal" declarations with optional initializer.
def foo(x, y=0): const len const pack=struct.pack, maxsize=1<<BPF ...
2. Same as 1, but using "as" instead of "=".
def foo(x, y=0): uses len, struct.pack as pack uses 1<<BPF as maxsize ...
3. Declaration is moved to function header. The keyword "given" is inspired by PEP 3150.
def foo(x, y=0) given len=len, pack=struct.pack, maxsize=1<<BPF: ...
4. Declaration is moved out of the function. The advantage is that bound names can be used to evaluate default values for actual parameters (it is useful to implement sentinel default value), and all expression are evaluated in natural order.
using len, struct.pack as pack, 1<<BPF as maxsize: def foo(x, y=0): ...
5. The least wordy syntax. No new keyword needed.
def foo(x, y=0; len=len, pack=struct.pack, maxsize=1<<BPF): ...
All above examples would be roughly equivalent to the following code:
def create(len=len, pack=struct.pack, maxsize=1<<BPF): def foo(x, y=0): ... return foo tmp = create() def foo(x, y=0): pass update_wrapper(tmp, foo) foo = tmp del create, tmp
This feature is rather ideologically opposite to Victor's approach.
Oh, only after sending my message I had read Scott's message about the asconstants decorator, that does just this optimization [1]. With this decorator above example can be written as: from codetransformer.transformers import asconstants @asconstants(len=len, pack=struct.pack, maxsize=1<<BPF) def foo(x, y=0): ... But it depends on bytecode implementation details. I wondering if it is worth to support this feature by syntax. [1] http://permalink.gmane.org/gmane.comp.python.ideas/36958