to be clear... when I said: "This is a break from dictionary syntax, but I guess it makes sense that the user needs to be explicit about adding new keys."
I meant "This is a break from [the old] dictionary syntax, but I guess it makes sense that the user needs to be explicit about adding new keys." On Wed, Feb 17, 2010 at 2:54 PM, Damien Moore <[email protected]> wrote: > Sorry for all of the questions. As you've probably gathered I'm a > little clueless about the XMP spec... > >> meta[key] always returns a {Exif,Iptc,Xmp}Tag object. That's a bit more code >> to write for application developers, but that's also much more flexible: a >> tag object contains more information than just a value. > > I understand that evaluating meta[key] (i.e. using __getitem__), > should return a *Tag object. But... > (thinking out loud) I'm not sure why meta[key]=value (i.e. > __setitem__) shouldn't be interpretable as > meta[key]=*Tag(key,value). For example: > > def __setitem__(self,key,value): > try: > #try setting the key assuming that value is a *Tag type > except TypeError: > tag_class=lookup_tag_type(key) > if value.__class__ != tag_class: > value=tag_class(key,value) > #try setting again > > Is the issue that lookup_tag_type is expensive? > > I agree that direct support for this is probably no big deal because I > can do what I need in helper functions. > >> should I assume that the user wants >> to set the value, or the raw_value? > > I guess always assume a value because that is how the *Tag __init__ > call works right? > If someone wants to do something more complicated they can use the full idiom. > >> if key in meta.xmp_keys: >> meta[key].value = value >> else: >> meta[key] = XmpTag(key, value) > > I gather this is also true for exif and iptc keys? This is a break > from dictionary syntax, but I guess it makes sense that the user needs > to be explicit about adding new keys. (Again, not a big deal, but > something that wasn't immediately obvious). I guess I don't like the > redundancy of having to refer to the key twice when adding it (invites > someone to try: meta[key1]=XmpTag(key2,value)). A simple alternative > would be: > > meta.add(XmpTag(key,value)) > > btw, setting the value property will update raw_value and vice versa right? > > >>> {'x-default': ['test2', 'test3']} >>> #works as expected >> >> Actually, it shouldn't. According to the XMP specification, the type of >> Xmp.dc.subject is "bag Text", meaning it expects a list of values, not a >> dictionary (it's not a LangAlt). > > So for key=="Xmp.dc.subject" this should work: > meta[key]=XmpTag(key,['test2','test3']) > > Please don't interpret these comments/questions as a request to change > anything. It's just taking a little bit to get my head around the new > API. > > cheers, > Damien > _______________________________________________ Mailing list: https://launchpad.net/~pyexiv2-developers Post to : [email protected] Unsubscribe : https://launchpad.net/~pyexiv2-developers More help : https://help.launchpad.net/ListHelp
