Creating type evaluation annotation

[dieter]

Marek Mosiewicz <marek.mosiewicz at jotel.com.pl> writes:
> ...
> I know that Python 3 has possibility to have indicate
> type for varibale or param
> What could be great to have possibility to annotate any 
> class with what I call "type evaluator" function.
> That could check method signature with rules specific 
> for given type.
> The simplest evaluator would simply check if signature
> is same as method definition. 
> But it could go futher. It could check whatever is valid 
> logic for creating methods in given class and whatever 
> are valid params for given method.
> Even more powerful evaluator could be not only
> valid/not valid indicator. It could validate
> and suggest next param or method part name for given
> written part of call. That could make python IDEs
> much more powerful
> From my experience having signature checking and
> hinting params when writing code is really big win.

You *can* do all that in Python -- even though you need
something beyond what Python typically comes with.

First, you need a formalisms to describe what should be checked.
There are various alternatives: I am using "zope.interface" (to
describe method signatures) and "zope.schema" (to describe
the "type" of attributes).

Next, you need something that does the checking.
Again, there are alternatives. I prefer to check things
in test suites -- and not permanently during productive use.
But, Python has the powerfull "metaclass" concept.
A metaclass allows you to customize class construction
and e.g. to instrument all defined methods to perform automatic
checks.