On 28.02.2017 15:46, Michel Desmoulin wrote: > lazy is not only practical, but it's also beautiful. It reads well. It > solves a problem we all have on a regular basis.
The only practical use case I ever ran into for lazy evaluation are lazy imports, simply because imports cause a lot of startup overhead. It's a case which the new keyword wouldn't help with, though. For the discussion, it would help if you'd write up a definition of where the lazy evaluation should finally happen, which use cases would be allowed or not and how the compiler could detect these. IMO, there are much better ways to write code which only evaluates expensive code when really needed. I don't see how "lazy" could automate this in a well defined, helpful and obvious way, simply because the side effects of moving evaluation from the place of definition to an arbitrary other place in the code are not easy to manage. Even if you do manage to clearly define when to evaluate a lazy expression, the context in which it gets evaluated may have already changed, giving wrong results, causing exceptions due to missing information. Delaying exceptions can also break the exception handling in your application. PS: You run into the same issues with lazy imports, which is why special care has to be taken when using these. -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Experts (#1, Feb 28 2017) >>> Python Projects, Coaching and Consulting ... http://www.egenix.com/ >>> Python Database Interfaces ... http://products.egenix.com/ >>> Plone/Zope Database Interfaces ... http://zope.egenix.com/ ________________________________________________________________________ ::: We implement business ideas - efficiently in both time and costs ::: eGenix.com Software, Skills and Services GmbH Pastor-Loeh-Str.48 D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg Registered at Amtsgericht Duesseldorf: HRB 46611 http://www.egenix.com/company/contact/ http://www.malemburg.com/ _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
