On Tuesday, September 5, 2017 at 6:42:07 PM UTC+5:30, Gregory Ewing wrote: > Steve D'Aprano wrote: > > The third entity is the reference linking the name to the object (the > > arrow). > > This isn't a runtime value in Python, nor is it a compile time entity that > > exists in source code. It is pure implementation, and as such, exists > > outside > > of the Python domain. > > The fact that there is a connection between the name and the > object is very much part of Python's abstract semantics. > > There are different ways to implement that connection, but > *any* implementation of Python has to include *some* > representation of it. > > There are also different words that can be used to describe > it. You can say that names are bound to objects, or that > names refer to objects, or that names hold references to > objects. These are all equally good ways of talking about > the exact same abstract concept. > > To me this argument about whether Python has references > or not is like an American person saying that cars have > hoods, and a British person saying he's wrong, hoods > are an implementation detail and cars actually have > bonnets instead.
Also called playing humpty-dumpty I believe there is a germ of value behind all this empty polemics There are 3 equivalence relations: 1. == — mathematical, too coarse to understand nuances of python semantics 2. is — machine representation, too fine to be useful 3. graph (or topological) equality which experienced pythonistas have internalized in understanding when two data structures are same or different [Roughly Anton's diagrams that are beyond my drawing capability!] And yet pythonistas need that to understand python data structures >>> a = [1,2] >>> b = [a,a] >>> c = [[1,2],[1,2]] >>> b == c True >>> b is c False >>> p = [1,2] >>> q = [p,p] >>> r = [[1,2],[1,2]] >>> q == r True >>> q is r False >>> b == q True >>> b == r True >>> b is q False >>> b is r False Now the pythonista understands that b and c may be math-= but have different structure Whereas b is graph-equal to q And c is graph-equal to r However there is no available operation to show/see that distinction The trouble is that graph-isomorphism is NP-complete so the crucial operation cannot be reasonably implemented Let the endless threads continue 😈 -- https://mail.python.org/mailman/listinfo/python-list
