Structures

[Paulo J. Matos]

Hi all,

I am a Python beginner, reading through 2.6 tutorial. I am wondering
where are structures?

On the other hand, I think I might have the answer. Since Python focus
on having one way to do it and structures are something like classes
with only public methods, if I want structures that's what I should use.
Is that right?

Cheers,
--
Paulo Jorge Matos - pocmatos at gmail.com
Webpage: http://www.personal.soton.ac.uk/pocm

[bearophileHUGS@lycos.com]

Re: Structures

Paulo J. Matos:

Since Python focus
on having one way to do it and structures are something like classes
with only public methods, if I want structures that's what I should use.
Is that right?

Yes, it is. On the other hand in Python 2.6 there's something that
helps you build one of such classes in a standard and handy way: see
"namedtuple " in the standard "collection s" module.

Bye,
bearophile

[Ben Finney]

Re: Structures

"Paulo J. Matos" <pocmatos@gmail .comwrites:

I am a Python beginner, reading through 2.6 tutorial. I am wondering
where are structures?

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.

[…] structures are something like classes with only public methods

Care to say more about what they are, not what they're like?

--
\ “Pinky, are you pondering what I'm pondering?” “Yes Brain, but |
`\ if our knees bent the other way, how would we ride a bicycle?” |
_o__) —_Pinky and The Brain_ |
Ben Finney

[Paulo J. Matos]

Re: Structures

On Mon, Nov 3, 2008 at 12:32 PM, Ben Finney
<bignose+hate s-spam@benfinney. id.auwrote:

"Paulo J. Matos" <pocmatos@gmail .comwrites:
>

>I am a Python beginner, reading through 2.6 tutorial. I am wondering
>where are structures?

>
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.
>

>[…] structures are something like classes with only public methods

>
Care to say more about what they are, not what they're like?
>

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. Still, answering your rhetoric question, a structure is way to
gather information by fields and those fields are referenced by name.
The fact that python 2.6 has now named tuples is a breath of fresh
air!

--
\ "Pinky, are you pondering what I'm pondering?" "Yes Brain, but |
`\ if our knees bent the other way, how would we ride a bicycle?" |
_o__) —_Pinky and The Brain_ |
Ben Finney
--

http://mail.python.org/mailman/listinfo/python-list

>
>
>

--
Paulo Jorge Matos - pocmatos at gmail.com
Webpage: http://www.personal.soton.ac.uk/pocm

[Ben Finney]

Re: Structures

"Paulo J. Matos" <pocmatos@gmail .comwrites:

On Mon, Nov 3, 2008 at 12:32 PM, Ben Finney
<bignose+hate s-spam@benfinney. id.auwrote:

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.

So no, the question was entirely honest and not a rhetorical device.

Still, answering your rhetoric question, a structure is way to
gather information by fields and those fields are referenced by
name.

Okay, you're talking about ‘struct’ from the C language. That helps
answer the question.

In Python, the way to do that is with a dict. A class can be used, but
is often overkill if one doesn't need customised behaviour.

The fact that python 2.6 has now named tuples is a breath of fresh
air!

That works also, but a dict will be more broadly useful; and
compatible with any Python version.

--
\ “Creativity can be a social contribution, but only in so far as |
`\ society is free to use the results.” —Richard Stallman |
_o__) |
Ben Finney

[Jorgen Grahn]

Re: Structures

On Mon, 3 Nov 2008 20:33:45 +0000, Paulo J. Matos <pocmatos@gmail .comwrote:

On Mon, Nov 3, 2008 at 12:32 PM, Ben Finney
<bignose+hate s-spam@benfinney. id.auwrote:

>"Paulo J. Matos" <pocmatos@gmail .comwrites:

....

>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.
>>

>>[?] structures are something like classes with only public methods

>>
>Care to say more about what they are, not what they're like?

>
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.

You're right. But the explanation you gave above, "classes with only
public methods", is C++-specific, and also fairly misleading ... there
is no real difference in C++ between struct Foo {}; and a class Foo
{}; it's just shorthand for class Foo { public: }; and struct Foo {
private: }; respectively.

/Jorgen

--
// Jorgen Grahn <grahn@ Ph'nglui mglw'nafh Cthulhu
\X/ snipabacken.se R'lyeh wgah'nagl fhtagn!

[Arnaud Delobelle]

Re: Structures

Ben Finney <bignose+hate s-spam@benfinney. id.auwrites:

"Paulo J. Matos" <pocmatos@gmail .comwrites:

[...]

Okay, you're talking about ‘struct’ from the C language. That helps
answer the question.

Note that structs are mutable.

In Python, the way to do that is with a dict. A class can be used, but
is often overkill if one doesn't need customised behaviour.
>

>The fact that python 2.6 has now named tuples is a breath of fresh
>air!

But isn't mutable, so it doesn't seem to be what you (Paulo) need.

That works also, but a dict will be more broadly useful; and
compatible with any Python version.

And is mutable.

--
Arnaud

[Aaron Brady]

Re: Structures

On Nov 3, 3:45 pm, Ben Finney <bignose+hate s-s...@benfinney. id.au>
wrote:

"Paulo J. Matos" <pocma...@gmail .comwrites:
>

On Mon, Nov 3, 2008 at 12:32 PM, Ben Finney
<bignose+hate s-s...@benfinney. id.auwrote:

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

[Craig Allen]

Re: Structures

>

Care to say more about what they are, not what they're like?
>

I'm not the OP and I may be biased by C++, I can imagine the
complaints when I say, classes are just structures with function
members for working on the structure.

[Arnaud Delobelle]

Re: Structures

Craig Allen <callen314@gmai l.comwrites:

>>
>Care to say more about what they are, not what they're like?
>>

>
I'm not the OP and I may be biased by C++, I can imagine the
complaints when I say, classes are just structures with function
members for working on the structure.

In C++ classes and structures are the same, except that class members
are private by default and structure members are public by default

--
Arnaud

[Paulo J. Matos]

Re: Structures

On Mon, Nov 3, 2008 at 10:10 PM, Arnaud Delobelle
<arnodel@google mail.comwrote:

Ben Finney <bignose+hate s-spam@benfinney. id.auwrites:
>

>"Paulo J. Matos" <pocmatos@gmail .comwrites:

[...]

>Okay, you're talking about 'struct' from the C language. That helps
>answer the question.

>
Note that structs are mutable.
>

Ah... :( That's a no go!

>In Python, the way to do that is with a dict. A class can be used, but
>is often overkill if one doesn't need customised behaviour.
>>

>>The fact that python 2.6 has now named tuples is a breath of fresh
>>air!

>
But isn't mutable, so it doesn't seem to be what you (Paulo) need.
>

What's then the reason for adding named tuples if they are not mutable...???

>That works also, but a dict will be more broadly useful; and
>compatible with any Python version.

>
And is mutable.
>

Even though I can use dicts where the keys are strings (as if it were
the name of the field), it seems to heavy, since a structure doesn't
need to be resizable (and dicts are) and it has constant time access
(which depending on the implementation I would guess dicts don't
have).

Can someone please clarify?

Cheers,

Paulo

--
Arnaud
--

http://mail.python.org/mailman/listinfo/python-list

>
>
>

--
Paulo Jorge Matos - pocmatos at gmail.com
Webpage: http://www.personal.soton.ac.uk/pocm

[Paulo J. Matos]

Re: Structures

On Mon, Nov 3, 2008 at 10:19 PM, Aaron Brady <castironpi@gma il.comwrote:

On Nov 3, 3:45 pm, Ben Finney <bignose+hate s-s...@benfinney. id.au>
wrote:

>"Paulo J. Matos" <pocma...@gmail .comwrites:
>>

On Mon, Nov 3, 2008 at 12:32 PM, Ben Finney
<bignose+hate s-s...@benfinney. id.auwrote:
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.

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?]


--
Paulo Jorge Matos - pocmatos at gmail.com
Webpage: http://www.personal.soton.ac.uk/pocm

[Joe Strout]

Re: Structures

On Nov 3, 2008, at 4:38 PM, Paulo J. Matos wrote:

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?

Classes.

Best,
- Joe

[Paulo J. Matos]

Re: Structures

On Mon, Nov 3, 2008 at 11:47 PM, Joe Strout <joe@strout.net wrote:

On Nov 3, 2008, at 4:38 PM, Paulo J. Matos wrote:
>

>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?

>
Classes.
>

ok, so that goes back to what I said on my first post. Classes with no
private fields/methods.

Thanks,

Paulo

Best,
- Joe
>
>
--

http://mail.python.org/mailman/listinfo/python-list

>
>
>

--
Paulo Jorge Matos - pocmatos at gmail.com
Webpage: http://www.personal.soton.ac.uk/pocm

[George Sakkis]

Re: Structures

On Nov 3, 6:51 pm, "Paulo J. Matos" <pocma...@gmail .comwrote:

On Mon, Nov 3, 2008 at 11:47 PM, Joe Strout <j...@strout.ne twrote:

On Nov 3, 2008, at 4:38 PM, Paulo J. Matos wrote:

>

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?

>

Classes.

>
ok, so that goes back to what I said on my first post. Classes with no
private fields/methods.

Technically there are no private attributes in (pure) Python so the
answer is still classes.

George