Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #84100

Re: Trees

Show key headers only | View raw

On 1/20/2015 4:47 PM, Mario wrote:
> In article <d34dbfbe-fe82-47dc-8bc3-c8773e2b70dd@googlegroups.com>,
> rustompmody@gmail.com says...
>>
>> Yeah python has trees alright.
>>
>> Heres' some simple tree-code
>
> Didn't you just demonstrate that Python has no trees and instead you
> have to implement them yourself (or use a third-party implementation)?
>
> I don't know what's the point of all this vain and misleading play with
> words.

It is not play with words. A tree is a recursive - nested - hierachical 
data structure with the restriction of no cycles or alternate pathways. 
  Python collections whose members are general objects, including 
collections, can be nested.  The resulting structures *are* tree 
structures, if not more general directed graphs.  They are quite 
commonly used in Python.

The common question -- "How do I flatten a list" -- is asking "How to I 
turn a list from a tree (or DAG, but not a cyclic graph*) into a 
sequence of leaf objects".  The question illustrates what is missing - 
builtin functions or methods for nested collections.  I already 
suggested that there *might* be a useful addition in this direction.

* A Python interpreter needs to take special measures to even display an 
infinitely recursive list without raising or even segfaulting.  Most 
posted 'flatten' functions do not account for this possibility.

 >>> l = [1]
 >>> l.append(l)
 >>> l
[1, [...]]


 > Not only most languages don't implement trees in their standard
> libraries

Typically, built-in collection type C has members of type M that does 
not include type C.  Therefore a C instance cannot (directly) contain a 
C instance.  The result is that people write a 'design pattern' to 
overcome the limitation and enable a C to indirectly include a C.  Since 
this limitations does not exist in Python's generalized collections of 
objects, the pattern is unneeded in Python.

-- 
Terry Jan Reedy

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Re: Trees Terry Reedy <tjreedy@udel.edu> - 2015-01-20 01:08 -0500
  Re: Trees Marko Rauhamaa <marko@pacujo.net> - 2015-01-20 11:45 +0200
    Re: Trees Paul Rubin <no.email@nospam.invalid> - 2015-01-20 10:14 -0800
      Re: Trees Marko Rauhamaa <marko@pacujo.net> - 2015-01-20 22:26 +0200
    Re: Trees Stephen Hansen <me+python@ixokai.io> - 2015-01-20 23:56 -0800
      Re: Trees Marko Rauhamaa <marko@pacujo.net> - 2015-01-21 10:35 +0200
      Re: Trees Rustom Mody <rustompmody@gmail.com> - 2015-01-21 04:09 -0800
        Re: Trees Chris Angelico <rosuav@gmail.com> - 2015-01-21 23:35 +1100
          Re: Trees Rustom Mody <rustompmody@gmail.com> - 2015-01-21 07:24 -0800
        Re: Trees Tim Chase <python.list@tim.thechases.com> - 2015-01-21 06:55 -0600
        Re: Trees Chris Angelico <rosuav@gmail.com> - 2015-01-22 00:01 +1100
        Re: Trees Tim Chase <python.list@tim.thechases.com> - 2015-01-21 08:26 -0600
        Re: Trees Chris Angelico <rosuav@gmail.com> - 2015-01-22 01:31 +1100
        Re: Trees Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-22 01:47 +1100
          Re: Trees Ian Kelly <ian.g.kelly@gmail.com> - 2015-01-21 09:15 -0700
          Re: Trees Ian Kelly <ian.g.kelly@gmail.com> - 2015-01-21 10:27 -0700
  Re: Trees Rustom Mody <rustompmody@gmail.com> - 2015-01-20 05:33 -0800
    Re: Trees Rustom Mody <rustompmody@gmail.com> - 2015-01-20 05:51 -0800
    Re: Trees Marko Rauhamaa <marko@pacujo.net> - 2015-01-20 16:15 +0200
      Re: Trees Rustom Mody <rustompmody@gmail.com> - 2015-01-20 06:35 -0800
    Re: Trees Ian Kelly <ian.g.kelly@gmail.com> - 2015-01-20 10:19 -0700
      Re: Trees Rustom Mody <rustompmody@gmail.com> - 2015-01-20 10:15 -0800
        Re: Trees Rustom Mody <rustompmody@gmail.com> - 2015-01-20 10:35 -0800
    Re: Trees Mario <marfig@gmail.com> - 2015-01-20 22:47 +0100
      Re: Trees Rustom Mody <rustompmody@gmail.com> - 2015-01-20 17:23 -0800
        Re: Trees Paul Rubin <no.email@nospam.invalid> - 2015-01-20 17:49 -0800
          Re: Trees Rustom Mody <rustompmody@gmail.com> - 2015-01-20 18:03 -0800
            Re: Trees Paul Rubin <no.email@nospam.invalid> - 2015-01-21 14:27 -0800
              Re: Trees Rustom Mody <rustompmody@gmail.com> - 2015-01-21 21:17 -0800
        Re: Trees Ian Kelly <ian.g.kelly@gmail.com> - 2015-01-21 15:54 -0700
          Re: Trees Rustom Mody <rustompmody@gmail.com> - 2015-01-21 21:20 -0800
            Re: Trees Ian Kelly <ian.g.kelly@gmail.com> - 2015-01-22 00:01 -0700
            Re: Trees Ian Kelly <ian.g.kelly@gmail.com> - 2015-01-21 23:56 -0700
          Re: Trees Paul Rubin <no.email@nospam.invalid> - 2015-01-21 23:16 -0800
            Re: Trees Rustom Mody <rustompmody@gmail.com> - 2015-01-22 08:54 -0800
      Re: Trees Terry Reedy <tjreedy@udel.edu> - 2015-01-20 21:19 -0500
        Re: Trees Mario Figueiredo <marfig@gmail.com> - 2015-01-21 14:05 +0000

csiph-web