check if class really implements api?

[Karsten W.]

Hello,
with the zope.interface module I can query if my class claims to
implement my API. This
is what the method implementedBy is for.

However, I find myself constantly changing the API and I am looking for
a more reliable way
to check my implementation classes. Is there a way to check if at least
all function
names of the API are defined by the class and if their parameter lists
fit the API? A way
to test this would save me a lot of time..

Kind regards,
Karsten.

[Heiko Wundram]

Re: check if class really implements api?

Karsten W. wrote:[color=blue]
> However, I find myself constantly changing the API and I am looking for
> a more reliable way
> to check my implementation classes. Is there a way to check if at least
> all function
> names of the API are defined by the class and if their parameter lists
> fit the API? A way
> to test this would save me a lot of time..[/color]

To make it short: no, there is no reliable way to test this.

To make it longer: yes, you can, with several kludges (and limitations),
test this sort of thing. For example, start by running a dir() on the
interface definition class, and for each name you get returned check
whether it is a callable/function, then in case it is, have a look at the
corresponding class claiming to implement the interface, check if the name
exists, if it is a callable, and whether the method signature is
appopriately similar.

Most of the latter can be done using the introspection support present in
Python, which is nicely wrapped up for you in a module and whose
documentation you can find at:

http://www.python.org/doc/2.4.2/lib/module-inspect.html

Be aware that this does not check for methods which might be added at
runtime to a class, that you might have to create more elaborate tests to
check whether a class that might be callable has the correct method
signature, and several other quirks (such as a function in the interface
prototype taking five arguments, whereas in the class definition taking
only a single catch-all argument).

See how much of a can of worm this is? That's why you should rely on
duck-typing: if it quacks like a duck and walks like a duck, chances are
you really have a duck. And the only reliable way to test that is to let it
run.

--- Heiko.

[Terry Hancock]

Re: check if class really implements api?

On 3 Jan 2006 12:56:58 -0800
"Karsten W." <DonQuixoteVonL aMancha@gmx.net > wrote:[color=blue]
> with the zope.interface module I can query if my class
> claims to implement my API. This
> is what the method implementedBy is for.
>
> However, I find myself constantly changing the API and I
> am looking for a more reliable way
> to check my implementation classes. Is there a way to
> check if at least all function
> names of the API are defined by the class and if their
> parameter lists fit the API? A way
> to test this would save me a lot of time..[/color]

You want:

Zope 2.5.1:
Interface.verif y.verify_class_ implementation

or

Zope 3.x:
zope.interface. verify

You'll want to read the source modules for documentation and
usage, as I don't think these are particularly well
documented anywhere else.

They are somewhat different in API between the two interface
implementations , but both do essentially the same thing --
they check the class against the interface object. This
will only tell you whether the methods are there and have
the same calling profile -- it obviously can't tell you
whether they do what you expect (or indeed do anything at
all).

But I had the same problem you're having, and I found them
useful.

Cheers,
Terry

--
Terry Hancock (hancock@Anansi Spaceworks.com)
Anansi Spaceworks http://www.AnansiSpaceworks.com

[Karsten W.]

Re: check if class really implements api?


Terry Hancock schrieb:
[color=blue]
> You want:
>[/color]
[...][color=blue]
> Zope 3.x:
> zope.interface. verify
>[/color]

This is exactly what I was looking for! There is a function verifyClass
and there is
a TestCase for verify.py which teaches how to use it.

Thanks a lot!
Karsten.