Source code for bokeh.application.handlers.function

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# Copyright (c) 2012 - 2021, Anaconda, Inc., and Bokeh Contributors.
# All rights reserved.
#
# The full license is in the file LICENSE.txt, distributed with this software.
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''' Provide a Bokeh Application Handler to build up documents by running
a specified Python function.

This Handler is not used by the Bokeh server command line tool, but is often
useful if users wish to embed the Bokeh server programmatically:

.. code-block:: python

    def make_doc(doc: Document):
        # do work to modify the document, add plots, widgets, etc.
        return doc

    app = Application(FunctionHandler(make_doc))

    server = Server({'/bkapp': app}, io_loop=IOLoop.current())
    server.start()

For complete examples of this technique, see
:bokeh-tree:`examples/howto/server_embed`

'''

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# Boilerplate
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from __future__ import annotations

import logging # isort:skip
log = logging.getLogger(__name__)

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# Imports
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# Standard library imports
from typing import Callable

# Bokeh imports
from ...document import Document
from ...util.callback_manager import _check_callback
from .handler import Handler, handle_exception

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# Globals and constants
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__all__ = (
    'FunctionHandler',
)

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# General API
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# Dev API
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ModifyDoc = Callable[[Document], None]

[docs]class FunctionHandler(Handler): ''' A Handler that accepts a plain python function to use for modifying Bokeh Documents. For example, the following code configures a handler with a function that adds an empty plot to a Document: .. code-block:: python def add_empty_plot(doc: Document): p = figure(x_range=(0, 10), y_range=(0, 10)) doc.add_root(p) return doc handler = FunctionHandler(add_empty_plot) This handler could be configured on an Application, and the Application would run this function every time a new session is created. .. autoclasstoc:: ''' _func: ModifyDoc _trap_exceptions: bool _safe_to_fork: bool
[docs] def __init__(self, func: ModifyDoc, *, trap_exceptions: bool = False) -> None: ''' Args: func (callable) : a function to modify and return a Bokeh Document. The function should have the form: .. code-block:: python def func(doc: Document): # modify doc return doc and it should return the passed-in document after making any modifications in-place. trap_exceptions (bool) : should exceptions in `func` be caught and logged or allowed to propagate ''' super().__init__() _check_callback(func, ('doc',)) self._func = func self._trap_exceptions = trap_exceptions self._safe_to_fork = True
# Properties -------------------------------------------------------------- @property def safe_to_fork(self) -> bool: ''' Whether it is still safe for the Bokeh server to fork new workers. ``False`` if ``modify_doc`` has already been called. ''' return self._safe_to_fork # Public methods ----------------------------------------------------------
[docs] def modify_document(self, doc: Document) -> None: ''' Execute the configured ``func`` to modify the document. After this method is first executed, ``safe_to_fork`` will return ``False``. ''' try: self._func(doc) except Exception as e: if self._trap_exceptions: handle_exception(self, e) else: raise finally: self._safe_to_fork = False
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