On Wed, 2009-11-04 at 19:18 -0600, Hartmut Kaiser wrote:
On Wed, Nov 4, 2009 at 6:34 PM, Steve Fisher <dr.s.m.fisher@gmail.com> wrote:
Just a note to remind people that the dictionary syntax in python is just a convenience - you need to implement __setitem__, __getitem__, __delitem__ etc. Our __setitem__ can reject requests to set fields whoch don't already exist for those cases where the set of attributes is not extensible. It just needs a private method called by the implementation to set the attributes with any defalt values and indicate whether or not it is extensible. I think it is best to try it and see if there are any practical problems. Also see: http://docs.python.org/library/userdict.html#module-UserDict which may be useful.
It is certainly doable from the technical point of view. My question is what would be the advantages of having a dict-like interface? Would that be in this form then:
If I rember the discussion from Banff correctly, the proposal was more like
jobDescription.attributes["Executable"] = "/bin/hostname"
Why not:
jobDescription["Executable"] = "/bin/hostname"
Yes, I'd also prefer this. Much shorter, and it resembles that a job description IS-A Attributes.
to decouple the attributes from the object properties. The dictionary seems to offer a reasonable interface for atributes, so why not use it?
not sure if one can then argue why not to use
jobDescription.attributes.Executable = "/bin/hostname"
Not good as we have no way to ensure only proper attributes are accessed. For instance
jobDescription.attributes.Executable1 = "/bin/hostname"
will go unnoticed as Python simply creates a member Executable1 assigning the string.
Ah, I did not know this! Hmm, that would indeed be a very good reason not to use Python properties for attributes.
One question about both approaches though, and to also about both approaches you list below: how would async ops be realized?
Async ops are separate and have to follow the get_attribute/set_attribute interface (which should be implemented in addition anyways)
... which gives more than one way to set/get attributes. I'm not sure what is more 'Pythonic': providing exactly one way to access attributes (i.e. via set_/get_attribute), or to provide a language-specific construct (dictionaries) as well. Technically, providing a dict interface as well seems entirely possible. It seems more a matter of taste whether to use them or not, especially since SAGA attributes are more restrictive than a normal dict. best, Mathijs