decorator to fetch arguments from global objects

[andrea crotti]

2013/6/18 Terry Reedy <tjreedy at udel.edu>

> On 6/18/2013 5:47 AM, andrea crotti wrote:
>
>> Using a CouchDB server we have a different database object potentially
>> for every request.
>>
>> We already set that db in the request object to make it easy to pass it
>> around form our django app, however it would be nice if I could set it
>> once in the API and automatically fetch it from there.
>>
>> Basically I have something like
>>
>> class Entity:
>>       def save_doc(db)
>>
>
> If save_doc does not use an instance of Entity (self) or Entity itself
> (cls), it need not be put in the class.


I missed a self it's a method actually..


>
>
>           ...
>>
>> I would like basically to decorate this function in such a way that:
>> - if I pass a db object use it
>> - if I don't pass it in try to fetch it from a global object
>> - if both don't exist raise an exception
>>
>
> Decorators are only worthwhile if used repeatedly. What you specified can
> easily be written, for instance, as
>
> def save_doc(db=None):
>   if db is None:
>     db = fetch_from_global()
>   if isinstance(db, dbclass):
>     save_it()
>   else:
>     raise ValueError('need dbobject')
>
>
>
Yes that's exactly why I want a decorator, to avoid all this boilerplate
for every function method that uses a db object..
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