Nick Coghlan wrote:
On Wed, Apr 25, 2012 at 7:41 PM, M.-A. Lemburg <mal@egenix.com> wrote:
Nick Coghlan wrote:
On Wed, Apr 25, 2012 at 10:55 AM, Steven D'Aprano <steve@pearwood.info> wrote:
In my opinion, this is an attractive nuisance.
-1 on the feature.
Agreed (and my preferred idiom for all the cited cases is also "always define the Python version, override at the end with the accelerated version").
IMO, defining things twice in the same module is not a very Pythonic way of designing Python software.
Left aside the resource leakage, it also makes if difficult to find the implementation that actually gets used, bypasses "explicit is better than implicit", and it doesn't address possible side-effects of the definitions that you eventually override at the end of the module.
Python is normally written with a top-to-bottom view in mind, where you don't expect things to suddenly change near the end.
This is why we introduced decorators before the function definition, rather than place them after the function definition. It's also why we tend to put imports, globals, helpers at the top of the file.
I agree overwriting at the end isn't ideal, but I don't think allowing returns at module level is a significant improvement. I'd rather see a higher level approach that specifically set out to tackle the problem of choosing between multiple implementations of a module at runtime that cleanly supported *testing* all the implementations in a single process, while still having one implementation that was used be default.
Isn't that an application developer choice to make rather than one that we force upon the developer and one which only addresses a single use case (having multiple implementation variants in a module) ? What about other use cases, where you e.g. * know that the subsequent function/class definitions are going to fail, because your runtime environment doesn't provide the needed functionality ? * want to limit the available defined APIs based on flags or other settings ? * want to make modules behave more like functions or classes ? * want to debug import loops ? Since the module body is run more or less like a function or class body, it seems natural to allow the same statements available there in modules as well. Esp. with the new importlib, tapping into the wealth of functionality in that area has become a lot easier than before. Only the compiler is preventing it. -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Source (#1, Apr 25 2012)
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