Archived discussions · Captured October 28, 2026

FunctionHandler v RootHandler

acooke.orgDec 24, 2018 #1

Both FunctionHandler and RootHandler have similar names, but they seem to be different conceptually (one is a server view and the other an application handler).

I have code that uses the Bokeh server to “push” a (non-interactive) plot to the browser. The code looks like:

def show(log, plot):

def modify_doc(doc):
    doc.add_root(plot)

app = Application(FunctionHandler(modify_doc))
server = Server(app)
server.start()
log.info('Opening Bokeh application on http://localhost:5006/')
server.io_loop.add_callback(server.show, "/")
server.io_loop.call_later(5, server.io_loop.stop)
server.io_loop.start()

and works fine. However, it’s kinda ugly. So I tried something like:

def modify_doc(doc):
    doc.add_root(plot)
    doc.template_variables['title'] = 'Hello World'
    doc.template = '''a template here based on FILE'''

which didn’t have the effect I expected. In fact, the template wasn’t used at all. Instead, my FunctionHandler seems to be being rendered(? wrapped?) by RootHandler using app_index.html.

Hence the question. Where does RootHandler come from? How can I either avoid it or modify it?

I feel like I’m missing something in the docs - I haven’t found anything that’s a fairly high-level overview that explains RootHandler.

(I realise I could use a file-system based application and this wouldn’t be an issue. Am I dumb to want to do this in Python?)

Thanks,

Andrew

PS And thanks for an interesting toolkit.

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BryanDec 24, 2018 #2

RootHandler is a Tornado view handler that handles incoming HTTP requests to "/" on a Bokeh server. It's called a "handler" because that is the conventional terminology Tornado adopts for things that handle incoming requests. RootHandler just shows a list of all the currently running apps on a Bokeh server, and only if you don't also install your own app on "/" (which would take precedence).

But Bokeh has its own kinds of entirely different and unrelated "handlers". Specifically, ApplicationHanders (such as FunctionHandler), that handle creating instances of a Bokeh application. The term "handler" is one example (of many) of a term this is highly overloaded across different projects and languages.

In any case setting a template in the manner below works for me on Bokeh 1.0.2 so you will need to provide more information in order to investigate: version information, a complete script, including the template, and any data needed to run.

BTW is has not been necessary to create an Application and FunctionHandler explicitly for a long time. You can just pass the function directly:

server = Server({'/': modify_doc})

as demonstrated in all the examples here:

https://github.com/bokeh/bokeh/tree/master/examples/howto/server_embed

Those examples also demonstrate another way to apply a template by using the server_document function explicitly.

Thanks,

Bryan

···

On Dec 24, 2018, at 08:34, acooke.org@gmail.com wrote:

Both FunctionHandler and RootHandler have similar names, but they seem to be different conceptually (one is a server view and the other an application handler).

I have code that uses the Bokeh server to "push" a (non-interactive) plot to the browser. The code looks like:

def show(log, plot):

    def modify_doc(doc):
        doc.add_root(plot)

    app = Application(FunctionHandler(modify_doc))
    server = Server(app)
    server.start()
    log.info('Opening Bokeh application on http://localhost:5006/'\)
    server.io_loop.add_callback(server.show, "/")
    server.io_loop.call_later(5, server.io_loop.stop)
    server.io_loop.start()

and works fine. However, it's kinda ugly. So I tried something like:

    def modify_doc(doc):
        doc.add_root(plot)
        doc.template_variables['title'] = 'Hello World'
        doc.template = '''a template here based on FILE'''

which didn't have the effect I expected. In fact, the template wasn't used at all. Instead, my FunctionHandler seems to be being rendered(? wrapped?) by RootHandler using app_index.html.

Hence the question. Where does RootHandler come from? How can I either avoid it or modify it?

I feel like I'm missing something in the docs - I haven't found anything that's a fairly high-level overview that explains RootHandler.

(I realise I could use a file-system based application and this wouldn't be an issue. Am I dumb to want to do this in Python?)

Thanks,
Andrew

PS And thanks for an interesting toolkit.

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andrew_cookeDec 25, 2018 #3

Thanks! That was enough for me to work out what I was confused about.

You're right that the template is being used. I was testing it via
the "title" template variable, but it turns out that something later
in the load process (maybe javascript?) is setting the page title to
"Bokeh Application" (that is what I thought was coming from
app_index.html and RootHandler).

Anyway, page title doesn't matter. I can still use the template for
what I need.

Thanks again,
Andrew

···

On Mon, Dec 24, 2018 at 09:44:47AM -0800, Bryan Van de ven wrote:

Hi

RootHandler is a Tornado view handler that handles incoming HTTP requests to "/" on a Bokeh server. It's called a "handler" because that is the conventional terminology Tornado adopts for things that handle incoming requests. RootHandler just shows a list of all the currently running apps on a Bokeh server, and only if you don't also install your own app on "/" (which would take precedence).

But Bokeh has its own kinds of entirely different and unrelated "handlers". Specifically, ApplicationHanders (such as FunctionHandler), that handle creating instances of a Bokeh application. The term "handler" is one example (of many) of a term this is highly overloaded across different projects and languages.

In any case setting a template in the manner below works for me on Bokeh 1.0.2 so you will need to provide more information in order to investigate: version information, a complete script, including the template, and any data needed to run.

BTW is has not been necessary to create an Application and FunctionHandler explicitly for a long time. You can just pass the function directly:

server = Server({'/': modify_doc})

as demonstrated in all the examples here:

https://github.com/bokeh/bokeh/tree/master/examples/howto/server_embed

Those examples also demonstrate another way to apply a template by using the server_document function explicitly.

Thanks,

Bryan

> On Dec 24, 2018, at 08:34, acooke.org@gmail.com wrote:
>
> Both FunctionHandler and RootHandler have similar names, but they seem to be different conceptually (one is a server view and the other an application handler).
>
> I have code that uses the Bokeh server to "push" a (non-interactive) plot to the browser. The code looks like:
>
> def show(log, plot):
>
> def modify_doc(doc):
> doc.add_root(plot)
>
> app = Application(FunctionHandler(modify_doc))
> server = Server(app)
> server.start()
> log.info('Opening Bokeh application on http://localhost:5006/'\)
> server.io_loop.add_callback(server.show, "/")
> server.io_loop.call_later(5, server.io_loop.stop)
> server.io_loop.start()
>
> and works fine. However, it's kinda ugly. So I tried something like:
>
> def modify_doc(doc):
> doc.add_root(plot)
> doc.template_variables['title'] = 'Hello World'
> doc.template = '''a template here based on FILE'''
>
> which didn't have the effect I expected. In fact, the template wasn't used at all. Instead, my FunctionHandler seems to be being rendered(? wrapped?) by RootHandler using app_index.html.
>
> Hence the question. Where does RootHandler come from? How can I either avoid it or modify it?
>
> I feel like I'm missing something in the docs - I haven't found anything that's a fairly high-level overview that explains RootHandler.
>
> (I realise I could use a file-system based application and this wouldn't be an issue. Am I dumb to want to do this in Python?)
>
> Thanks,
> Andrew
>
> PS And thanks for an interesting toolkit.
>
> --
> You received this message because you are subscribed to the Google Groups "Bokeh Discussion - Public" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to bokeh+unsubscribe@continuum.io.
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> To view this discussion on the web visit https://groups.google.com/a/continuum.io/d/msgid/bokeh/b728eb14-0f3d-4f44-9876-49db7930bfa8%40continuum.io\.
> For more options, visit https://groups.google.com/a/continuum.io/d/optout\.

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systemJul 21, 2021 #4

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