Bokeh - Models must be owned by only a single document [error]

Question

Trying to build a dashboard with multiple pages using Flask/Bokeh combination. The code that I use for main file (test.py) collects(imports) all the files corresponding to pages of the dashboard.

# test.py
from page1 import Page1

app = Flask(__name__)
app.config.from_envvar('FLASKR_SETTINGS', silent=True)


class Dashboard(object):
    def __init__(self, *pages):
        self._pages = [page(self) for page in pages]

    def __call__(self, doc):
        tabs = []
        for page in self._pages:
            tabs.append(Panel(child=page.layout, title=page.title))
        doc.add_root(Tabs(tabs=tabs))


bkapp = Application(FunctionHandler(Dashboard(Page1)))

The intent is to define each page of the dashboard in its own file which, eventually, is imported in the main file(test.py) and served by an webserver (gunicorn, for example).

# page1.py                                                                                                                                                 from bokeh.models.widgets import Select
from bokeh.layouts import column, gridplot, widgetbox, layout, row

class Page(object):

    title = "Override in subclass"

    def __init__(self, dashboard):
        self._dash = dashboard
        self._layout = None

    @property
    def layout(self):

        if self._layout is None:
            self._layout = self._make_layout()
        return self._layout

    def _make_layout(self):
        raise NotImplementedError("subclasses must define")


class Page1(Page):
    title = "Page1"

    def _make_layout(self):
        self.sim_prod = Select(title="Selection:",
                               value="Yes",
                               options=["Yes", "No"]
                               )
        self.x = row(self.sim_prod)
        self.layout1 = layout([ [self.x] ], sizing_mode='scale_width')
        return self.layout1

    def some_callback(self, attr, old, new):
    # to be defined later
        pass

The widget(Select, in this case) is built and served properly (see picture) but an error is generated when trying to reload the page:

Error:

   raise RuntimeError("Models must be owned by only a single document, %r is already in a doc" % (self))
RuntimeError: Models must be owned by only a single document, WidgetBox(id='04f8b890-e3ca-48d9-954d-c33b96e80c78', ...) is already in a doc
ERROR:tornado.access:500 GET /bkapp/autoload.js?bokeh-autoload-element=8ca7bf9a-0c4f-462c-97f9-1f6b1a246628&bokeh-app-path=/bkapp&bokeh-absolute-url=http://127.0.0.1:60624/bkapp (127.0.0.1) 233.03ms
[2018-05-01 10:17:20 -0700] [94201] [DEBUG] GET /

Any suggestion how to fix it, greatly appreciated! I'm using Python 3.6 and Bokeh 0.12.15.

Cheers,

Answer 1

In case someone else bumps into the same issue, changing the layout method of Page class, as shown below, re-creates the layout every time the page is reloaded.

class Page(object):

    title = "Override in subclass"

    def __init__(self, dashboard):
        self._dash = dashboard
        self._layout = None

    @property
    def layout(self):
        return self._make_layout()

    def _make_layout(self):
        raise NotImplementedError("subclasses must define")