On Thu, 17 Aug 2017 10:14 am, Ned Batchelder wrote:
> the name/value data model of > Python is not some trivial detail that we could change to match some > other language: it's a fundamental part of what makes Python what it is. It is also an evaluation model which matches nearly all of the most popular languages of the last two decades, including Java[1], Ruby, (I think) PHP, and Javascript. > For some reason, students have been taught that things can be either > call-by-reference or call-by-value. But those are not the only two > possibilities, and neither completely describes how Python works. > > Learn Python for what it is. > > --Ned. Indeed. The insistence on this false dichotomy of call by value versus by reference puzzles me, since alternatives go back to one of earliest, and most influential, programming languages: Lisp. Algol, another early and hugely influential language, used call by name. Its like there was an entire generation of cooks and chefs who insisted that there are only two ways of cooking food: steaming, and barbecuing, and came up with elaborate rationalisations for why frying, roasting, boiling etc are actually one of the two. [1] Despite the obnoxious insistence of Java experts that it is "pass by value", where the value they are talking about is not the actual value, but some hidden, implementation-dependent pointer or reference to the value: http://javadude.com/articles/passbyvalue.htm In the words of the Effbot Fredrik well, I guess you can, in theory, value an artificial number assigned to an object as much as the object itself. "Joe, I think our son might be lost in the woods" "Don't worry, I have his social security number" http://www.effbot.org/zone/call-by-object.htm It absolutely astonishes me how the Java community abuse the term "call by value" in this way, despite the confusion it causes, and despite knowing the correct answer. Scott Stanchfield actually does know what is going on. Despite the inflammatory title of his post, and the outright false comment right at the start: "Java is strictly pass-by-value, exactly as in C." deep in the article linked above, he comes clean and writes: "A correct statement would be /Object references are passed by value/." [emphasis /.../ in original] But the objects themselves are not, as would be required by pass-by-value semantics. So he knows that the values, the objects themselves, are not copied when you pass them to a function. Only the invisible references to the objects are copied, but they are not the values anyone cares about. The example he shows has precisely the same behaviour as the equivalent Python code. -- Steve “Cheer up,” they said, “things could be worse.” So I cheered up, and sure enough, things got worse. -- https://mail.python.org/mailman/listinfo/python-list
