On Fri, Jun 5, 2015 at 11:29 PM, Rustom Mody <rustompm...@gmail.com> wrote: > On Friday, June 5, 2015 at 4:36:35 PM UTC+5:30, Steven D'Aprano wrote: >> On Fri, 5 Jun 2015 01:16 pm, Rustom Mody wrote: >> > The abstract platonic immutable list is non-existent in python >> >> Just pretend that "immutable list" is spelled "tuple". > > Ok lets say I make no fuss about the need to 'pretend'. > > And I try... > >>>> a=[1,2,3] >>>> b=(a,a) >>>> a > [1, 2, 3] >>>> b > ([1, 2, 3], [1, 2, 3]) >>>> a.append(4) >>>> b > ([1, 2, 3, 4], [1, 2, 3, 4])
Congrats! You just proved that an object can itself be immutable, but can contain references to mutables. Ain't that awesome? Did you have a point? > It was an analogy. > C programmers use lists all right all the time. > However until they see something like python, they dont know that they never > REALLY saw lists. ie lists in python are more first-class than C. If you're talking about the things C programmers use all the time, they're not linked lists, they're arrays - identified by base pointer and element count. Linked lists are common in LISPy languages, but not all that common in C, nor C-derived APIs. Most APIs designed for C usage are either array-based or generator-based. http://www.gnu.org/software/libc/manual/html_node/Scanning-Directory-Content.html Array-based: scandir accepts a pointer-to-pointer, which it populates with a pointer to freshly-allocated data, and it returns the number of entries stashed there. http://www.gnu.org/software/libc/manual/html_node/Opening-a-Directory.html http://www.gnu.org/software/libc/manual/html_node/Reading_002fClosing-Directory.html Generator-based: opendir returns a generator, readdir gives the next result or NULL http://www.gnu.org/software/libc/manual/html_node/Array-Sort-Function.html Array-based: pass it a base pointer and a count (and an object size, since it's completely generic), and it sorts the elements. Your point is still broadly valid, though; these arrays are not first-class objects. They do have their own little quirks; so long as the original array isn't deallocated, you can efficiently work with views by simply using a base pointer inside the original array and a length that's shorter than the whole array. Very convenient if you need it, but most certainly not first-class lists, and can cause problems if you're not careful. Python lists truly are first-class objects; "more first-class than C" in the sense that 1 is more true than 0. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
