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comp.lang.python

python interfaces

hyperboreean

1/4/2008 3:00:00 PM

Hi,
Probably it has been asked before, but I'll still ask.
Why doesn't python provide interfaces trough its standard library? Or it
was ever proposed to be included in the language?
Zope's implementation seems pretty flexible and straightforward.

Thanks.
10 Answers

Michele Simionato

1/4/2008 3:23:00 PM

0

On Jan 4, 3:59 pm, hyperboreean <hyperbore...@nerdshack.com> wrote:
> Hi,
> Probably it has been asked before, but I'll still ask.
> Why doesn't python provide interfaces trough its standard library? Or it
> was ever proposed to be included in the language?
> Zope's implementation seems pretty flexible and straightforward.
>
> Thanks.

Python 3.0 will introduce Abstract Base Classes:

http://www.python.org/dev/peps...

Sion Arrowsmith

1/4/2008 5:01:00 PM

0

hyperboreean <hyperboreean@nerdshack.com> wrote:
>Why doesn't python provide interfaces trough its standard library?

Because they're pointless. Java interfaces are a hack around the
complexities of multiple inheritence. Python does multiple
inheritence Just Fine (give or take the subtleties of super()) so
does not need them.

Interfaces used purely with the idea of type safety provide
precious little gain for the added clutter and inconvenience.
Compare them to Java's requirement for explicit declaration of
exceptions thrown in a method signature, if you will.

--
\S -- siona@chiark.greenend.org.uk -- http://www.chaos.org...
"Frankly I have no feelings towards penguins one way or the other"
-- Arthur C. Clarke
her nu becomeþ se bera eadward ofdun hlæddre heafdes bæce bump bump bump

Peter Maas

1/5/2008 8:30:00 PM

0

Sion Arrowsmith wrote:
> hyperboreean <hyperboreean@nerdshack.com> wrote:
>> Why doesn't python provide interfaces trough its standard library?
>
> Because they're pointless.

Wrong. I'm using Eclipse with the Java Development Tools (JDT) who do
a wonderful job using interfaces to perform lots of checking, warning
and code generation *nearly in real time while I am editing my code*.
Because JDT knows interfaces it knows what to do and to suggest. An
interface is a software specification allowing you to use a software
package without extensive code studies. This is a good thing.

> Java interfaces are a hack around the complexities of multiple
> inheritence.

A hack is something applied subsequently to solve a software problem while
avoiding large changes. Java interfaces originate from careful language
design. You are free to dislike Java interfaces but calling them a hack is
just plain wrong.

Once software becomes really big interfaces are very useful to handle
complexity. Ever wondered why the Zope people introduced interfaces in
their Python code?

> Interfaces used purely with the idea of type safety provide
> precious little gain for the added clutter and inconvenience.

An interface is a software specification allowing you to use a software
package without extensive code studies. This is a good thing. Interfaces
have nothing to do with multiple inheritance. They just tell you how to
connect, how to plug in.

--
Regards/Gruesse,

Peter Maas, Aachen
E-mail 'cGV0ZXIubWFhc0B1dGlsb2cuZGU=\n'.decode('base64')

Peter Maas

1/5/2008 8:43:00 PM

0

Sion Arrowsmith wrote:
> hyperboreean <hyperboreean@nerdshack.com> wrote:
>> Why doesn't python provide interfaces trough its standard library?
>
> Because they're pointless.

Wrong. I'm using Eclipse with the Java Development Tools (JDT) who do
a wonderful job using interfaces to perform lots of checking, warning
and code generation *nearly in real time while I am editing my code*.
Because JDT knows interfaces it knows what to do and to suggest.

> Java interfaces are a hack around the complexities of multiple
> inheritence.

A hack is something applied subsequently to solve a software problem while
avoiding large changes. Java interfaces originate from careful language
design. You are free to dislike Java interfaces but calling them a hack is
just plain wrong.

Once software becomes really big interfaces are very useful to handle
complexity. Ever wondered why the Zope people introduced interfaces in
their Python code?

> Interfaces used purely with the idea of type safety provide
> precious little gain for the added clutter and inconvenience.

An interface is a software specification allowing you to use a software
package without extensive code studies. This is a good thing. Interfaces
have nothing to do with multiple inheritance and are not about type safety
in the first place. They just tell you how to connect, how to plug in.

--
Regards/Gruesse,

Peter Maas, Aachen
E-mail 'cGV0ZXIubWFhc0B1dGlsb2cuZGU=\n'.decode('base64')

r.grimm

1/6/2008 7:31:00 AM

0

On Jan 4, 6:01 pm, Sion Arrowsmith <si...@chiark.greenend.org.uk>
wrote:
> hyperboreean <hyperbore...@nerdshack.com> wrote:
> >Why doesn't python provide interfaces trough its standard library?
>
> Because they're pointless. Java interfaces are a hack around the
> complexities of multiple inheritence. Python does multiple
> inheritence Just Fine (give or take the subtleties of super()) so
> does not need them.
>
Hallo,
Interfaces are a extremly smart Design Principle in static typed
languages
like Java and C++.
C++ support Interfaces in a form of abstract base classes. They aren't
pointless.
They force the user of a framework to use it in a defined way. You
prescribe in
the base class the usage of a classsystem and allow only in derived
classes
to variate the behavior.
To appreciate Interfaces look at the Template Methode Pattern (http://
en.wikipedia.org/wiki/Template_method_pattern )
or especially at the Non Virtual Interface ( http://www.gotw.ca/publications/...
) Idiom from Herb Sutter.

To be short C++ support Interfaces and multiple inheritace.

Greetings Rainer

Fredrik Lundh

1/6/2008 10:01:00 AM

0

r.grimm@science-computing.de wrote:

> Interfaces are a extremly smart Design Principle in static typed
> languages like Java and C++.

that's somewhat questionable in itself, and even more questionable as an
argument for interfaces in Python.

I'd recommend anyone who thinks that they cannot program without formal
interfaces to try using Python as Python for a while, before they try
using it as something else. you might be surprised over how easy it is
to build robust stuff without having to add lots of extra constraints to
your code.

</F>

Carl Banks

1/6/2008 5:08:00 PM

0

On Sat, 05 Jan 2008 23:31:02 -0800, r.grimm wrote:
> They force the user of a framework to use it in a defined way.

This is the arrogance of the provider thinking that he can anticipate all
the needs of the user.

Even when interfaces exist, they should be there to guide the user rather
than to force the user. A user should be able to refuse to implement the
interface, if the user knows that full implmentation is not necessary, or
dangerous. Frankly, a lot of interfaces suck. The user is often a lot
smarter than the provider, and nearly always knows his needs better. My
sympathies in these matters are entirely on the user's side--I know
that's very different from the philosophies of languages like C++ and
Java.

There's a time and a place for interfaces. Your average run-of-the-mill
polymorphism is not it. Usually interfaces are more of a burden than a
benefit, especially in code that is young and still subject to lots of
redesign and refactoring.

And ehen interfaces do make sense, such as in a plugin system or a
complex framework, the user should be free to ignore the interface at his
own risk.



Carl Banks

Bruno Desthuilliers

1/6/2008 7:44:00 PM

0

Sion Arrowsmith a écrit :
> hyperboreean <hyperboreean@nerdshack.com> wrote:
>
>>Why doesn't python provide interfaces trough its standard library?
>
>
> Because they're pointless.
(snip rant about Java's "interfaces")

Hem... Zope3's "interface" system is not exactly the same thing as
Java's one.

r.grimm

1/7/2008 7:33:00 AM

0

On Jan 6, 11:01 am, Fredrik Lundh <fred...@pythonware.com> wrote:
> r.gr...@science-computing.de wrote:
> > Interfaces are a extremly smart Design Principle in static typed
> > languages like Java and C++.
>
> that's somewhat questionable in itself, and even more questionable as an
> argument for interfaces in Python.
>
> I'd recommend anyone who thinks that they cannot program without formal
> interfaces to try using Python as Python for a while, before they try
> using it as something else. you might be surprised over how easy it is
> to build robust stuff without having to add lots of extra constraints to
> your code.
>
> </F>
Hallo,
I argued, that Interface and multiple inheritance are different
things and
especially, that Interfaces are very useful in staticially typed
languages.
In such languages like Java and C++ you need a formalismen to guide
the user.
You may call it extension point, pure virtual function or abstract
methode.

Sorry for the misunderstanding, I argued for Interface in heavyweight
static
typed languages and nor for lightweight dynamic typed languages like
python.
They aren't pointless and a hack.

Greetings Rainer

Sion Arrowsmith

1/7/2008 1:06:00 PM

0

Bruno Desthuilliers <bdesth.quelquechose@free.quelquepart.fr> wrote:
>Sion Arrowsmith a écrit :
>(snip rant about Java's "interfaces")
>
>Hem... Zope3's "interface" system is not exactly the same thing as
>Java's one.

Yeah, I was in need of letting off some steam in general and
didn't pay enough attention that what I was ranting about was
on topic. Given that Zope3's "interfaces" are the kind of thing
under discussion, the correct response is obviously Michele's
pointing at the ABC PEP.

--
\S -- siona@chiark.greenend.org.uk -- http://www.chaos.org...
"Frankly I have no feelings towards penguins one way or the other"
-- Arthur C. Clarke
her nu becomeþ se bera eadward ofdun hlæddre heafdes bæce bump bump bump