Nick, On 2016-01-20 1:37 AM, Nick Coghlan wrote:
On 20 January 2016 at 10:38, Chris Angelico<rosuav@gmail.com> wrote:
Big one for the bike-shedding: Is this "capture as local" (the same semantics as the default arg - if you rebind it, it changes for the current invocation only), or "capture as static" (the same semantics as a closure if you use the 'nonlocal' directive - if you rebind it, it stays changed), or "capture as constant" (what people are usually going to be doing anyway)? The "shared value" approach can already be achieved by binding a mutable object rather than an immutable one, and there's no runtime speed difference between looking up a local and looking up a constant, so I think it makes sense to just stick with "default argument semantics, but without altering the function signature"
One possible name for such a directive would be "sharedlocal": it's in most respects a local variable, but the given definition time initialisation value is shared across all invocations to the function.
With that spelling:
def f(*, len=len): ...
Would become:
def f(): sharedlocal len=len
FWIW I strongly believe that this feature (at least the "len=len"-like optimizations) should be implemented as an optimization in the interpreter. We already have "nonlocal" and "global". Having a third modifier (such as sharedlocal, static, etc) will only introduce confusion and make Python less comprehensible. Yury