Interface Implementation in Python

[p_shakil@yahoo.com]

Hi,

I would like to know the interface concept in Python.How the
Interface is defined and implemented in Python?.

How to access the interface fromn Client?

Thanks
PSB

[MonkeeSage]

Re: Interface Implementation in Python

On Mar 5, 6:25 pm, p_sha...@yahoo. com wrote:

Hi,
>
I would like to know the interface concept in Python.How the
Interface is defined and implemented in Python?.
>
How to access the interface fromn Client?
>
Thanks
PSB

Not sure exactly what you mean, but in python (like most dynamic
languages) an "interface" is simply a behavioral type system. Any
object can implement an interface, based on its signature. For
example; let's say you have a file object which implements read() and
write(). Any other object with a sufficiently similar signature (e.g.,
StringIO), can be said to implement the same interface. An interface
in python is simply a specified behavior, and any object which
implements that behavior can be said to have the same "interface" .

HTH,
Jordan

[Johannes Woolard]

Re: Interface Implementation in Python

'Lo, I think I know what you're asking:

I would like to know the interface concept in Python.How the
Interface is defined and implemented in Python?.

I assume you're talking about the what Java calls an interface - and
the simple answer is that we don't have an equivalent in Python.
This is because in the Python system of classes, interface inheritance
would be unenforceable (because methods can be arbitrarily added at
runtime).

How to access the interface fromn Client?

I'm not completely sure what you mean here... client class, client of
some protocol? Assuming you mean the client class, my answer above
should suffice (and if not then I am completely missing the question).

Regards,

Johannes Woolard

[Larry Bates]

Re: Interface Implementation in Python

p_shakil@yahoo. com wrote:

Hi,
>
I would like to know the interface concept in Python.How the
Interface is defined and implemented in Python?.
>
How to access the interface fromn Client?
>
Thanks
PSB
>

You might want to look at how Zope 3 implements interfaces.

http://wiki.zope.org/zope3/FrontPage

http://wiki.zope.org/zope3/programmers_tutorial.pdf

-Larry

[=?ISO-8859-1?Q?BJ=F6rn_Lindqvist?=]

Re: Interface Implementation in Python

On 5 Mar 2007 16:25:03 -0800, p_shakil@yahoo. com <p_shakil@yahoo .comwrote:

Hi,
>
I would like to know the interface concept in Python.How the
Interface is defined and implemented in Python?.
>
How to access the interface fromn Client?

You have a class with methods and data. You write many unit tests for
that class which defines the behaviour of your interface. Make sure
your class passes all those tests. When you are done, not only does
your unit tests specify an interface, you also have a concrete class
that implements that interface.

Now replace the original class with another class. If that class also
passes all your tests, then you can conclude that it also implements
the same interface.

--
mvh Björn

[Goldfish]

Re: Interface Implementation in Python

I would like to know the interface concept in Python.How the

Interface is defined and implemented in Python?.

One way I have implemented interfaces, is as follows:

class MyInterface(obj ect):
def someMethod(self , argument):
raise NotImplementedE rror()

If anybody ever uses that class directly, or subclasses it without
implementing a real version of that method, a runtime error can be
expected. This bridges both interfaces and abstract classes.

As others have pointed out, this isn't quite like a Java interface,
but I have found it useful to state my intentions up front, and that
is how I do it. The only way to truly enforce this is by following up
with lots of good test cases, run often.

[p_shakil@yahoo.com]

Re: Interface Implementation in Python

On Mar 6, 11:55 am, "Goldfish" <gregt...@minds pring.comwrote:

I would like to know the interface concept in Python.How the
Interface is defined and implemented in Python?.

>
One way I have implemented interfaces, is as follows:
>
class MyInterface(obj ect):
def someMethod(self , argument):
raise NotImplementedE rror()
>
If anybody ever uses that class directly, or subclasses it without
implementing a real version of that method, a runtime error can be
expected. This bridges both interfaces and abstract classes.
>
As others have pointed out, this isn't quite like a Java interface,
but I have found it useful to state my intentions up front, and that
is how I do it. The only way to truly enforce this is by following up
with lots of good test cases, run often.

I have a class by name Point3D in Python.

class Point3D :
def __int(self):
self.__x =0.0
self.__y =0.0
self.__z =0.0

def setPoint(x,y,z) :
self.__x =x
self.__y =y
self.__z =z

def getPoint(x,y,z) :
x = self.__x
y = self.__y
z = self.__z

I dont want to expose the above Point3D implementation to the user /
client side.To achieve that we can use interface concept.In Python to
use interface concept.

How the interface class looks like for Point3D in python?.

How to implement that Interface?

How to access the implemented interface thru Interface Object in the
client side?

It will be helpful if somebody proivide a piece of sample code for
creating the interface for the above access at the client place

in C++ these can be done in this way

class IPoint : public IUnknown{
virtual void setPoint(int x,int y,int z)=0;
virtual void getPoint(&x,&y, &z)=0;
}

class Point3D: public IPoint {
private :
float _x ,_y,_z;
public:
void Point3D() {
_x=_y=_z =0
}
void setPoint(int x,int y,int z){

_x =x
_y =y
_z =z


}
void getPoint(&x,&y, &z){
x = _x
y = _y
z = _z
}
}

Access the Point data in the client side

IPoint *pIPoint = NULL;
pISampleInterfa ce = CoCreateInstanc e(..);
............... .
pISampleInterfa ce ->QueryInstance( IID_IPoint ,(void*&)pIPoin t )

// We have the pIPoint interafce
float dX =0,dY=0,dZ=0;

pIPoint->setPoint(10,20 ,30);

pIPoint->getPoint(&dX ,&dY,&dZ);

printf ( "%f,%f%f",d X ,dY,dZ);

10.0 20.0 30.0


Thanks
PSB

--------------------------------------------------------------------------------

[MonkeeSage]

Re: Interface Implementation in Python

On Mar 6, 6:23 pm, p_sha...@yahoo. com wrote:

I dont want to expose the above Point3D implementation to the user /
client side.To achieve that we can use interface concept.In Python to
use interface concept.

In python you would use name mangling to hide parts of the interface
from the public.

class Point3D:
def __init__(self):
self.__x = 0.0
self.__y = 0.0
self.__z = 0.0

def __setPoint(x,y, z):
self.__x = x
self.__y = y
self.__z = z

def __getPoint(x,y, z):
x = self.__x
y = self.__y
z = self.__z

p = Point3D()
p.__setPoint(1, 2,3)

# ...
# AttributeError: Point3D instance has no attribute '__setPoint'

Regards,
Jordan