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Re: What the Pythons docs means by "container" ?

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On 17Feb2015 13:21, candide <c.candide@laposte.net> 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.
>--------------------------

And this is the basic thing, as you understand.

>So containers contain : what a great definition!

Shrug. It is a useful descriptive term when you want to talk about things. You 
might keep in mind that a "container"'s _primary_ purpose is usually its 
containing function. So a list. But not so some arbitrary object, even though 
most objects have references to 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
[...]
>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 !

You might find it duck types like other containers.

[...]
>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).

Duck typing again: this bases the term on behaviour, not memory use.

>So a file is a container ? recall a file supports the in operator :

Yes and no. A file can be iterated. "in" on a file reads the file as a side 
effect of iterating over it. A generator also supports "in", again by 
iteration.

Neither of these things has a .__contains__ method; the "in" operator falls 
back to iteration if there is no .__contains__.

A container usually lets you test "in" in a nondestructive/nonconsuming 
fashion. An iterable can be "in"ed, but it will be consumed. So iterables are 
not, of themselves, containers.

So, range? A range object knows its bounds and state; it can answer "in" 
without consuming the range iteration, so it is effectively a container.

Hoping this helps.

Cheers,
Cameron Simpson <cs@zip.com.au>

[Alain] had been looking at his dashboard, and had not seen me, so I
ran into him. - Jean Alesi on his qualifying prang at Imola '93

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What the Pythons docs means by "container" ? candide <c.candide@laposte.net> - 2015-02-17 13:21 -0800
  Re: What the Pythons docs means by "container" ? Cameron Simpson <cs@zip.com.au> - 2015-02-18 08:39 +1100
    Re: What the Pythons docs means by "container" ? candide <c.candide@laposte.net> - 2015-02-17 16:30 -0800
      Re: What the Pythons docs means by "container" ? Chris Angelico <rosuav@gmail.com> - 2015-02-18 11:49 +1100
        Re: What the Pythons docs means by "container" ? candide <pascal.ortiz@gmail.com> - 2015-02-17 18:14 -0800
          Re: What the Pythons docs means by "container" ? MRAB <python@mrabarnett.plus.com> - 2015-02-18 18:04 +0000
          Re: What the Pythons docs means by "container" ? Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-18 11:50 -0700
          Re: What the Pythons docs means by "container" ? Ethan Furman <ethan@stoneleaf.us> - 2015-02-18 11:43 -0800
          Re: What the Pythons docs means by "container" ? Terry Reedy <tjreedy@udel.edu> - 2015-02-18 15:04 -0500
            Re: What the Pythons docs means by "container" ? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-19 10:03 +1100
              Re: What the Pythons docs means by "container" ? Ben Finney <ben+python@benfinney.id.au> - 2015-02-19 11:05 +1100
              Re: What the Pythons docs means by "container" ? Chris Angelico <rosuav@gmail.com> - 2015-02-19 11:33 +1100
  Re: What the Pythons docs means by "container" ? Terry Reedy <tjreedy@udel.edu> - 2015-02-17 19:54 -0500
  Re: What the Pythons docs means by "container" ? perfectican <perfectican@gmail.com> - 2015-02-19 02:59 -0800
    Re: What the Pythons docs means by "container" ? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-02-19 11:20 +0000
  Re: What the Pythons docs means by "container" ? Rustom Mody <rustompmody@gmail.com> - 2015-02-20 03:37 -0800
    Re: What the Pythons docs means by "container" ? Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-20 11:38 -0700

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