On Fri, Jun 8, 2012 at 12:18 PM, Larry Hastings <[email protected]> wrote: > On 06/07/2012 07:08 PM, Steven D'Aprano wrote: > > Perhaps func.__signature__ should be a computed the first time it is > accessed? > > > The PEP already declares that signatures are lazily generated. signature() > checks to see if __signature__ is set, and if it is returns it. (Or, > rather, a deepcopy of it, assuming we go down that route.) If __signature__ > isn't set, signature() computes it and returns that. (Possibly caching in > __signature__, possibly not, possibly caching the result then returning a > deepcopy.)
The need for a consistent return value ownership guarantee (i.e. "it's OK to mutate the return value of inspect.signature()") and the implicit inspect module guarantee of "introspection is non-intrusive and doesn't affect the internal state of inspected objects" are the main reasons I think implicit caching is a bad idea. However, there are also a couple of pragmatic reasons I don't like the idea: 1. It's unlikely there will be a huge performance difference between deep copying an existing Signature object and deriving a new one 2. If someone actually *wants* cached signature lookup for speed reasons and is willing to sacrifice some memory in order to do so (e.g. when using signatures for early parameter checking), they can just do: "cached_signature = functools.lru_cache(inspect.signature)" This approach will provide *genuine* caching, with no deep copying involved when the same callable is encountered a second time. You will also get all the benefits that the LRU caching mechanism provides, rather than having a hidden unbounded caching mechanism that potentially encompasses every function in the application. Cheers, Nick. -- Nick Coghlan | [email protected] | Brisbane, Australia _______________________________________________ Python-Dev mailing list [email protected] http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com