On Wednesday, February 18, 2015 at 2:51:34 AM UTC+5:30, candide wrote: > Official Python documentation very frequently invokes a mysterious > *container* data structure. The PLR manual explains : > > -------------------------- > Some objects contain references to other objects; these are called containers. > -------------------------- > > So containers contain : what a great definition! > > To be more precise, the "container" wording suggests a data structure > _storing_ items somewhere and that the number of items in the container has a > memory footprint. This is exacly the "container" definition given by the ISO > C++ standard (cf. > http://www.open-std.org/jtc1/sc22/open/n2356/lib-containers.html) : > > -------------------------- > Containers are objects that store other objects. > -------------------------- > > So I was considering a Python range object NOT being a container: indeed, > range(10**6) does NOT store 10**6 integers and range(10**6) has a small > memory footprint in the contrary to the associated list : > > ---------------------------------------------- > >>> from sys import getsizeof > >>> r = range(10**6) > >>> L = list(r) > >>> getsizeof(r) > 24 > >>> getsizeof(L) > 4500056 > >>> > ---------------------------------------------- > > Then, mining the official docs, I realized that the collections module > provides an ABC Container class allowing you to know if a given object is a > container or not. And what a surprise, a range object IS a container ! > > ---------------------------------------------- > >>> from collections import Container > >>> r = range(10**6) > >>> isinstance(r, Container) > >>> > True > > >>> > ---------------------------------------------- > > So, what documentation means by the generic term of "container"? > > I agree with the existence of built-in containers (list, dict and the like) > and the existence of special containers provided by the collections module > (most of them inheriting from a built-in container) but I can't find a > precise definition explaining what is a "container object" or a "container > type". > > The docs at : > > https://docs.python.org/3.2/reference/datamodel.html#object.__contains__ > > explains that a container is an object compatible with the membership test > (in and not in operators). So a file is a container ? recall a file supports > the in operator : > > ---------------------------------------------- > $ touch my_test.txt > $ python3.2 > Python 3.2.3 (default, Feb 28 2014, 00:22:33) > [GCC 4.7.2] on linux2 > Type "help", "copyright", "credits" or "license" for more information. > >>> 42 in open("my_test.txt") > False > >>> from collections import Container > >>> isinstance(open("my_test.txt"), Container) > False > >>> > ----------------------------------------------
+1 See https://www.python.org/dev/peps/pep-0246/ There Guido says "something much better is about to happen" Best as I know its not happened yet... [Personal note: I am currently trying to teach python and the lack of a standardized place for all protocols (in python's duck typing sense) is quite a slow-down-er for me and my class ] -- https://mail.python.org/mailman/listinfo/python-list
