XMP support

[helgeerbe]

While implementing heic support to picframe, I had to find out that IPTC is not supported for heic images.

But IPTCcore is part of XMP. So I use XMP tags. If they are available they will override IPTC tags (e.g. for jpg images)

I used the following mapping:

• IPTC Keywords -> XMP subject
• IPTC Object Name -> XMP Headline (XMP Title is a valid tag. But Headline seems to be used more widely???)
• IPTC Caption/Abstract -> XMP description

The Pillow function xmp = image.getxmp() returns a dictionary of XMP Tags. Unfortunately the structure seems not to be fixed, so I implemented a recursive search for the tags. To make it more worse, I found images in the net, where sub dictionary elements are splitted in list elements.

I ended in this not so nice code. Do one of you have an idea fore a nicer and more robust code, to extract the tags? I tried to avoid using other libs (e. g. extracting the original xml structure and use something like xml.searchelement).

def __find_xmp_key(self, key, dic):
        for k, v in dic.items():
            if key == k:
                return v
            elif isinstance(v, dict):
                val = self.__find_xmp_key(key, v) 
                if val:
                    return val 
            elif isinstance(v, list):
                for x in v:
                    if isinstance(x, dict):
                        val = self.__find_xmp_key(key, x) 
                        if val:
                            return val 
        return None
    
    def __do_xmp_keywords(self, xmp):
        try:
            # title
            val = self.__find_xmp_key('Headline', xmp)
            if val and isinstance(val, str) and len(val) > 0:
                self.__tags['IPTC Object Name'] = val
            # caption
            try:
                val = self.__find_xmp_key('description', xmp)
                if val:
                    val = val['Alt']['li']['text']
                    if val and isinstance(val, str) and len(val) > 0:
                        self.__tags['IPTC Caption/Abstract'] = val
            except KeyError:
                pass
            # tags
            try: 
                val = self.__find_xmp_key('subject', xmp)
                if val:
                    val = val['Bag']['li']
                    if val and isinstance(val, list) and len(val) > 0:
                        tags = ''
                        for tag in val:
                            tags += tag +  ","
                        self.__tags['IPTC Keywords'] = tags 
            except KeyError:
                pass
        except Exception as e:
            self.__logger.warning("xmp loading has failed: %s -> %s", self.__filename, e)