Merge ed51de7 into cf2fc33

holoviews/core/dimension.py

@@ -1409,10 +1409,16 @@ def options(self, *args, **kwargs):
 
         from ..util import opts
         if options is None:
-            expanded = {}
+            expanded_backends = [({}, backend)]
+        elif isinstance(options, list): # List of Options objects
+            expanded_backends = opts._expand_by_backend(options, backend)
         else:
-            expanded = opts._expand_options(options, backend)
-        return self.opts(expanded, backend=backend, clone=clone)
+            expanded_backends = [(opts._expand_options(options, backend), backend)]
+
+        obj = self
+        for backend, expanded  in expanded_backends:
+            obj = obj.opts(expanded, backend=backend, clone=clone)
+        return obj
 
 
     def _repr_mimebundle_(self, include=None, exclude=None):

holoviews/core/options.py

@@ -583,7 +583,8 @@ class Options(param.Parameterized):
 
     _option_groups = ['style', 'plot', 'norm']
 
-    def __init__(self, key=None, allowed_keywords=[], merge_keywords=True, max_cycles=None, **kwargs):
+    def __init__(self, key=None, allowed_keywords=[], merge_keywords=True,
+                 max_cycles=None, backend=None, **kwargs):
 
         invalid_kws = []
         for kwarg in sorted(kwargs.keys()):
@@ -612,6 +613,7 @@ def __init__(self, key=None, allowed_keywords=[], merge_keywords=True, max_cycle
                             else Keywords(allowed_keywords))
         super(Options, self).__init__(allowed_keywords=allowed_keywords,
                                       merge_keywords=merge_keywords, key=key)
+        self.backend = backend
 
     def keywords_target(self, target):
         """
@@ -1932,7 +1934,7 @@ def set_options(cls, obj, options=None, backend=None, **kwargs):
         spec, compositor_applied = cls.expand_compositor_keys(options)
         custom_trees, id_mapping = cls.create_custom_trees(obj, spec)
         cls.update_backends(id_mapping, custom_trees, backend=backend)
-        
+
         # Propagate ids to the objects
         not_used = []
         for (match_id, new_id) in id_mapping:

holoviews/util/__init__.py

@@ -83,7 +83,9 @@ class opts(param.ParameterizedFunction):
        strict, invalid keywords prevent the options being applied.""")
 
     def __call__(self, *args, **params):
-        if params and not args:
+        if not params and not args:
+            return Options()
+        elif params and not args:
             return Options(**params)
 
         if len(args) == 1:
@@ -117,13 +119,13 @@ def apply_groups(cls, obj, options=None, backend=None, clone=True, **kwargs):
         simple format may be used, e.g.:
 
             opts.apply_groups(obj, style={'cmap': 'viridis'},
-                                         plot={'show_title': False})
+                                   plot={'show_title': False})
 
         If the object is nested the options must be qualified using
         a type[.group][.label] specification, e.g.:
 
             opts.apply_groups(obj, {'Image': {'plot':  {'show_title': False},
-                                                    'style': {'cmap': 'viridis}}})
+                                              'style': {'cmap': 'viridis}}})
 
         If no opts are supplied all options on the object will be reset.
 
@@ -244,6 +246,30 @@ def defaults(cls, *options, **kwargs):
         cls._linemagic(cls._expand_options(merge_options_to_dict(options)), backend=kwargs.get('backend'))
 
 
+    @classmethod
+    def _expand_by_backend(cls, options, backend):
+        "Given a list of Option objects, return a list of grouped backend"
+        groups = defaultdict(list)
+        used_fallback = False
+        for obj in options:
+            if obj is None: # Why are None's being supplied?
+                continue
+            elif obj.backend:
+                opts_backend = obj.backend
+            elif backend is None:
+                opts_backend = Store.current_backend
+                obj.backend= opts_backend
+            else:
+                opts_backend = backend
+                obj.backend = opts_backend
+                used_fallback = True
+            groups[opts_backend].append(obj)
+
+        if backend and not used_fallback:
+            cls.param.warning('Fallback backend specified but not used.')
+
+        return [(bk, cls._expand_options(o, bk)) for (bk, o) in groups.items()]
+
     @classmethod
     def _expand_options(cls, options, backend=None):
         """
@@ -410,7 +436,7 @@ def builder(cls, spec=None, **kws):
                 if reraise:
                     raise ValueError(prefix + msg)
 
-            return Options(spec, **kws)
+            return Options(spec, backend=backend, **kws)
 
         filtered_keywords = [k for k in completions if k not in cls._no_completion]
         kws = ', '.join('{opt}=None'.format(opt=opt) for opt in sorted(filtered_keywords))