Structures

[Glenn Linderman]

On approximately 11/3/2008 3:38 PM, came the following characters from 
the keyboard of Paulo J. Matos:
> On Mon, Nov 3, 2008 at 10:19 PM, Aaron Brady <castironpi at gmail.com> wrote:
>   
>> On Nov 3, 3:45 pm, Ben Finney <bignose+hates-s... at benfinney.id.au>
>> wrote:
>>     
>>> "Paulo J. Matos" <pocma... at gmail.com> writes:
>>>
>>>       
>>>> On Mon, Nov 3, 2008 at 12:32 PM, Ben Finney
>>>> <bignose+hates-s... at benfinney.id.au> wrote:
>>>>         
>>>>> I'm wondering a more fundamental question: What are structures?
>>>>> That is, what do *you* mean by that term; without knowing that, an
>>>>> answer isn't likely to be meaningful.
>>>>>           
>>>> Well, I guess that everyone pretty much gets since it exists in
>>>> every other language as struct, or define-structure, or whatever is
>>>> the syntax.
>>>>         
>>> Take care with broad sweeping statements about "every other language",
>>> or even "most other languages". They are usually flat-out wrong:
>>> there is a stunning variety of different approaches and concepts in
>>> programming languages, with very little common to even a majority of
>>> them.
>>>       
>> Yea, verily.  How many languages do you think that is?  Feel free to
>> count C and C++ as different ones.
>>
>> "Four shalt thou not count, neither count thou two...."
>> http://en.wikipedia.org/wiki/Holy_Hand_Grenade_of_Antioch#Usage_instructions
>>     
>
> Well, I wouldn't dare to say I know a lot of languages but the ones I
> do provide mechanisms to define structures / records: C, C++, Scheme,
> Common Lisp, Haskell, SML, Ocaml.
> This is obviously a minority if you count all available programming
> languages in the world, but I would dare to say these cover a lot of
> ground.
>   

There are languages that do not have structs; but usually there is some 
way to obtain something similar.

> However, I wouldn't dare to say Python needs structures to be a good
> language, or anything similar. My question was more directed to : if
> there aren't structures in Python, what do Pythonists use instead?
> (I have seen dicts might be an alternative, but as I said in previous
> post, they seem to flexible [making them a canon to shoot a fly, and
> they probably lack constant-time access, right?]
>   

Dicts have constant time access.  On the other hand, the constant is 
significantly larger than the constant for accessing a C struct.

Note that classes, by default, are based on a contained dict!  There are 
games to be played with slots that can apparently improve that.  I am 
not yet experienced enough with Python to know if a slot is as fast as a 
C struct, but perhaps it is.  You can have both slots and a dict, to get 
both speed and flexibility, or you can eliminate the dict and use slots 
only, but that limits your flexibility.  But structs aren't flexible, 
except at compile time, so that might not be a problem for you.

Another thing I don't know is if slots are as fast as tuples.  Perhaps a 
slots-only class and a tuple might be speed rivals?  But the former is 
mutable, and the latter not.

Perhaps a more experience Python user can answer that question, at least 
for some particular implementation.

-- 
Glenn -- http://nevcal.com/
===========================
A protocol is complete when there is nothing left to remove.
-- Stuart Cheshire, Apple Computer, regarding Zero Configuration Networking