On 17.11.2016 11:16, Mikhail V wrote: > Citation from > http://legacy.python.org/dev/peps/pep-0203/ > > """ > Expressions of the form > > <x> = <x> <operator> <y> > > are common enough in those languages to make the extra syntax > worthwhile, and Python does not have significantly fewer of those > expressions. Quite the opposite, in fact, since in Python you can > also concatenate lists with a binary operator, something that is > done quite frequently. Writing the above expression as > > <x> <operator>= <y> > > -> __is both more readable__ and less error prone, because it is > instantly obvious to the reader that it is <x> that is being > changed, and not <x> that is being replaced by something almost, > but not quite, entirely unlike <x>. > > """ > > Aha, sure, if "readable" == "suits C programmers". > And it's surely not, which in some sence also means that it *more* > error prone, since I cannot notice possible error so easy.
The above follows the general principle in Python that "explicit is better than implicit": 1. "a = a + 1" means (in Python): add 1 to a (via the .__add__() method) and bind the new value to "a". 2. "a += 1" means (in Python): let the object a add 1 to itself (via the .__iadd__() method) and bind the new value to "a". In the first variant, a may well result in a new object being created, even changing the object type. In the second variant, it is immediately clear that the intent is for a to do something to itself. It is much less likely to result in a new object type (even though it may still result in a new object being created). More common is to have a manipulate itself without even changing the object. Examples: --------- >>> l = [1,2,3] >>> id(l) 140431507775856 >>> l = l + [4] >>> id(l) 140431507776864 Here, a new list object was created. >>> l += [5] >>> id(l) 140431507776864 >>> Here, the object itself was manipulated without creating a copy; and that's what you'd typically expect from an in-place operation on mutable objects. The situation is different with immutable objects: >>> a = 1 >>> id(a) 27693400 >>> a = a + 1 >>> id(a) 27693376 >>> a += 1 >>> id(a) 27693352 In both cases, you get new objects (but the object type remains the same). -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Experts (#1, Nov 17 2016) >>> 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/
