Merge derpibooru tags

Disregard the fact that I'm using a class as if it were a singleton.

class Tag(dict):
    _byName = {}
    _byTagId = {}

    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        Tag._byName[kwargs["name"]] = self
        Tag._byTagId[kwargs["tagId"]] = self

        self.implications = TagSet([self])
        self._implications_collapsed = False

    def collapseImplications(self):
        if self._implications_collapsed:
            return
        self._implications_collapsed = True

        for tagT in list(self.implications):
            tagT.collapseImplications()
            self.implications.update(tagT.implications)

    def __hash__(self):
        return self["tagId"]

    @classmethod
    def fromName(cls, name):
        return Tag._byName[name]

    @classmethod
    def fromTagId(cls, tagId):
        return Tag._byTagId[tagId]

    @classmethod
    def allTags(self):
        return list(Tag._byName.values())

    @classmethod
    def addEquivalence(cls, s, t):
        tagS = Tag.fromTagId(s)
        tagT = Tag.fromTagId(t)

        combined = TagSet()
        combined.update(tagS.implications)
        combined.update(tagT.implications)

        tagS.implications = combined
        tagT.implications = combined

    @classmethod
    def addImplication(cls, s, t):
        tagS = Tag.fromTagId(s)
        tagT = Tag.fromTagId(t)
        tagS.implications.add(tagT)

def loadTags(cursor):
    cursor.execute("select id, name, description, image_count from public.tags")
    for tagId, name, description, imageCount in cursor.fetchall():
        Tag(tagId=tagId, name=name, description=description, imageCount=imageCount)

    cursor.execute("select tag_id, target_tag_id from public.tag_aliases")
    for s, t in cursor.fetchall():
        Tag.addEquivalence(s, t)

    cursor.execute("select tag_id, target_tag_id from public.tag_implications")
    for s, t in cursor.fetchall():
        Tag.addImplication(s, t)

    for tag in Tag.allTags():
        tag.collapseImplications()
        tag['tagsetId'] = tag.implications.tagsetId

    return Tag._byTagId

def loadImageTaggings(cursor, images, tags):
    result = set()
    collectedTagsets = set()

    cursor.execute("select image_id, tag_id from public.image_taggings")
    for imageId, tagId in cursor.fetchall():
        if imageId not in images:
            continue

        image = Image.fromImageId(imageId)
        tag = tags[tagId]
        result.add((image['imageId'], tag['tagsetId']))

    return result