Property Multiplexer Example

gistfile1.py

class PropertyMultiplexer(EventDispatcher):
    select = ListProperty()

    def __init__(self, rule_sets, **kwargs):
        super(PropertyMultiplexer, self).__init__(**kwargs)
        self.rule_sets = rule_sets
        default = rule_sets.default
        
        # there must be a default in rule_sets and it
        # must define a default for each possible property
        for r, v in default.iteritems():
            self.create_property(r)
            setattr(self, r, v)

    def on_select(self, instance, keys):
        rsets = self.rule_sets
        rules = dict(rsets.default)

        # Merge from less specific to most specific
        key = None
        for k in keys:
            if key is not None:
                key = key + '_' + k
            else: 
                key = k
            rule_set = getattr(rsets, key, None)
            if rule_set:
                rules.update(rule_set)

        for r, v in rules.iteritems():
            setattr(self, r, v)


# because of button bar, many 1.6 devices will up less than 1.6 in 
# portrait and more than 1.6 in landscape
LANDSCAPE_ASPECT_RATIO_CUTOFF = 1.7
PORTRAIT_ASPECT_RATIO_CUTOFF = 1.6
# this will cut off slightly over galaxy note
# physical screen major dimension, 4.49in
TABLET_SIZE_CUTOFF = 4.75 

class LayoutMux(PropertyMultiplexer):
    def __init__(self, **kwargs):
        super(LayoutMux, self).__init__(**kwargs)
        Window.bind(size=self.detect)
        self.detect(Window, Window.size)
    
    def detect(self, win, size):
        w, h = map(float, size)
        ratio = h / w
        portrait = ratio > 1.
        
        if portrait:
            aspect = h / w
            major = h / Metrics.dpi 
            tall = aspect > LANDSCAPE_ASPECT_RATIO_CUTOFF
        else:
            aspect = w / h
            major = w / Metrics.dpi
            tall = aspect > PORTRAIT_ASPECT_RATIO_CUTOFF
        tablet =  major > TABLET_SIZE_CUTOFF

        orientation = 'portrait' if portrait else 'landscape'
        aspect = 'tall' if tall else 'short'
        size = 'tablet' if tablet else 'phone'

        select = (orientation, aspect, size)
        if select != self.select:
            Logger.debug('portrait: {}, tall: {}, tablet: {}'.format(
                orientation, aspect, size)
            )

        self.select = select

Nice and clean. :)