spec.py

class Spec:
    """ Wrapper around a dictionary with convenience functions for getting values.
        Specs are linked hierarchically, and the parent Spec is queried when the key
        is not found in the local dictionary.
    """

    def __init__(self, specDict, parentSpec):
        self.specDict = specDict
        self.parentSpec = parentSpec

    def get(self, key, default=None, doRecurse=True):
        """ Returns the value of the specified property in the current spec,
            or looks it up recursively in the parent spec when it is not found,
            or returns the property default if no match is found.
        """
        if key in self.specDict:
            return self.specDict[key]
        if self.parentSpec != None and doRecurse:
            return self.parentSpec.get(key, default)
        return default
    
    def getSpec(self, key, default=None, doRecurse=True):
        dict = self.get(key, default, doRecurse)
        return Spec(dict, self) if dict != None else None
    
    def getRootValue(self, key, default):
        """ Returns the value of the specified property in the root spec,
            or returns the property default if no match is found.
        """
        if self.parentSpec == None:
            return self.specDict.get(key, default)
        return self.parentSpec.getRootValue(key, default)

class ImageSpec(Spec):
    """ Spec with custom attributes.
    """

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.prevSpec = None
        self.frames = None
        self.nextTransitionDuration = 0