Provide Viewer baseclass (#2045)

panel/pane/base.py

@@ -44,6 +44,8 @@ def panel(obj, **kwargs):
     """
     if isinstance(obj, Viewable):
         return obj
+    elif hasattr(obj, '__panel__'):
+        return panel(obj.__panel__())
     if kwargs.get('name', False) is None:
         kwargs.pop('name')
     pane = PaneBase.get_pane_type(obj, **kwargs)(obj, **kwargs)

panel/pipeline.py

@@ -11,6 +11,7 @@
 from .widgets import Button, Select
 from .param import Param
 from .util import param_reprs
+from .viewable import Viewer
 
 
 class PipelineError(RuntimeError):
@@ -102,7 +103,7 @@ def get_breadths(node, graph, depth=0, breadths=None):
 
 
 
-class Pipeline(param.Parameterized):
+class Pipeline(Viewer):
     """
     A Pipeline represents a directed graph of stages, which each
     return a panel object to render. A pipeline therefore represents
@@ -222,6 +223,9 @@ def __init__(self, stages=[], graph={}, **params):
             self.add_stage(name, stage, **kwargs)
         self.define_graph(graph)
 
+    def __panel__(self):
+        return self.layout
+
     def _validate(self, stage):
         if any(stage is s for n, (s, kw) in self._stages.items()):
             raise ValueError('Stage %s is already in pipeline' % stage)
@@ -527,9 +531,6 @@ def tap_renderer(plot, element):
         )
         return plot
 
-    def _repr_mimebundle_(self, include=None, exclude=None):
-        return self.layout._repr_mimebundle_(include, exclude)
-
     #----------------------------------------------------------------
     # Public API
     #----------------------------------------------------------------

panel/viewable.py

@@ -769,3 +769,35 @@ def server_doc(self, doc=None, title=None, location=True):
         add_to_doc(model, doc)
         if location: self._add_location(doc, location, model)
         return doc
+
+
+class Viewer(param.Parameterized):
+    """
+    A baseclass for custom components that behave like a Panel object.
+    By implementing __panel__ method an instance of this class will
+    behave like the returned Panel component when placed in a layout,
+    render itself in a notebook and provide show and servable methods.
+    """
+
+    def __panel__(self):
+        """
+        Subclasses should return a Panel component to be rendered.
+        """
+        raise NotImplementedError
+
+    def servable(self, title=None, location=True):
+        return self.__panel__().servable(title, location)
+
+    servable.__doc__ = ServableMixin.servable.__doc__
+
+    def show(self, title=None, port=0, address=None, websocket_origin=None,
+             threaded=False, verbose=True, open=True, location=True, **kwargs):
+        return self.__panel__().show(
+            title, port, address, websocket_origin, threaded,
+            verbose, open, location, **kwargs
+        )
+
+    show.__doc__ = ServableMixin.show.__doc__
+
+    def _repr_mimebundle_(self, include=None, exclude=None):
+        return self.__panel__._repr_mimebundle_(include, exclude)