On 2017-09-08, Joshua Morton wrote: > In general this won't work. It's not generally possible to know if a given > statement has side effects or not.
That's true but with the AST static analysis, we find anything that has potential side effects. The question if any useful subset of real modules pass these checks. If we flag everything as no lazy import safe then we don't gain anything. > As an example, one normally wouldn't expect function or class > definition to have side effects, but if a function is decorated, > the decorators are evaluated at function "compilation"/import > time, and may have side effects. Decorators are handled in my latest prototype (module is not lazy). > As another example, one can put arbitrary expressions in a > function annotation, and those are evaluated at import time. Not handled yet but no reason they can't be. > As a result of this, you can't even know if an import is safe, > because that module may have side effects. That is, the module > foo.py: > > import bar > > isn't known to be lazy, because bar may import and start the logging > module, as an example. That is handled as well. We only need to know if the current module is lazy safe or not. Imports of submodules that have side-effects will have those side effects happen like they do now. The major challenge I see right now is 'from .. import' and class bases (i.e. metaclass behavior). If we do the safe thing then all from-imports make the module unsafe for lazy loading and any class definition that has a base class is also unsafe. I think the idea is not yet totally dead though. We could have a command-line option to enable it. Modules that depend on side-effects of from-import and from base classes could let the compiler know about that somehow (make it explicit). That would also a good fraction of modules to be lazy import safe. Regards, Neil _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
