Source code for bokeh.application.handlers.handler

#-----------------------------------------------------------------------------
# Copyright (c) 2012 - 2024, Anaconda, Inc., and Bokeh Contributors.
# All rights reserved.
#
# The full license is in the file LICENSE.txt, distributed with this software.
#-----------------------------------------------------------------------------
''' Provide a base class for Bokeh Application handler classes.

When a Bokeh server session is initiated, the Bokeh server asks the Application
for a new Document to service the session. To do this, the Application first
creates a new empty Document, then it passes this new Document to the
``modify_document`` method of each of its handlers. When all handlers have
updated the Document, it is used to service the user session.

Below is an example outline of a custom handler that might modify documents
based off information in some database:

.. code-block:: python

    class DatabaseHandler(Handler):
        """ A Bokeh Application handler to initialize Documents from a database

        """

        def modify_document(self, doc: Document) -> None:
            # do some data base lookup here to generate 'plot'

            # add the plot to the document (i.e modify the document)
            doc.add_root(plot)

'''

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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
#-----------------------------------------------------------------------------

# Standard library imports
import os
import sys
import traceback
from typing import TYPE_CHECKING, Any

# Bokeh imports
from ...document import Document
from ..application import ServerContext, SessionContext

if TYPE_CHECKING:
    from tornado.httputil import HTTPServerRequest

    from .code_runner import CodeRunner

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

#-----------------------------------------------------------------------------
# General API
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#-----------------------------------------------------------------------------
# Dev API
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[docs] class Handler: ''' Provide a mechanism for Bokeh applications to build up new Bokeh Documents. ''' _failed: bool _error: str | None _error_detail: str | None _static: str | None def __init__(self) -> None: self._failed = False self._error = None self._error_detail = None self._static = None # Properties -------------------------------------------------------------- @property def error(self) -> str | None: ''' If the handler fails, may contain a related error message. ''' return self._error @property def error_detail(self) -> str | None: ''' If the handler fails, may contain a traceback or other details. ''' return self._error_detail @property def failed(self) -> bool: ''' ``True`` if the handler failed to modify the doc ''' return self._failed @property def safe_to_fork(self) -> bool: return True # Public methods ----------------------------------------------------------
[docs] def modify_document(self, doc: Document) -> None: ''' Modify an application document in a specified manner. When a Bokeh server session is initiated, the Bokeh server asks the Application for a new Document to service the session. To do this, the Application first creates a new empty Document, then it passes this Document to the ``modify_document`` method of each of its handlers. When all handlers have updated the Document, it is used to service the user session. *Subclasses must implement this method* Args: doc (Document) : A Bokeh Document to update in-place Returns: Document ''' raise NotImplementedError("implement modify_document()")
[docs] def on_server_loaded(self, server_context: ServerContext) -> None: ''' Execute code when the server is first started. Subclasses may implement this method to provide for any one-time initialization that is necessary after the server starts, but before any sessions are created. Args: server_context (ServerContext) : ''' pass
[docs] def on_server_unloaded(self, server_context: ServerContext) -> None: ''' Execute code when the server cleanly exits. (Before stopping the server's ``IOLoop``.) Subclasses may implement this method to provide for any one-time tear down that is necessary before the server exits. Args: server_context (ServerContext) : .. warning:: In practice this code may not run, since servers are often killed by a signal. ''' pass
[docs] async def on_session_created(self, session_context: SessionContext) -> None: ''' Execute code when a new session is created. Subclasses may implement this method to provide for any per-session initialization that is necessary before ``modify_doc`` is called for the session. Args: session_context (SessionContext) : ''' pass
[docs] async def on_session_destroyed(self, session_context: SessionContext) -> None: ''' Execute code when a session is destroyed. Subclasses may implement this method to provide for any per-session tear-down that is necessary when sessions are destroyed. Args: session_context (SessionContext) : ''' pass
[docs] def process_request(self, request: HTTPServerRequest) -> dict[str, Any]: ''' Processes incoming HTTP request returning a dictionary of additional data to add to the session_context. Args: request: HTTP request Returns: A dictionary of JSON serializable data to be included on the session context. ''' return {}
[docs] def static_path(self) -> str | None: ''' Return a path to app-specific static resources, if applicable. ''' if self.failed: return None else: return self._static
[docs] def url_path(self) -> str | None: ''' Returns a default URL path, if applicable. Handlers subclasses may optionally implement this method, to inform the Bokeh application what URL it should be installed at. If multiple handlers specify ``url_path`` the Application will use the value from the first handler in its list of handlers. ''' return None
def handle_exception(handler: Handler | CodeRunner, e: Exception) -> None: ''' Record an exception and details on a Handler. ''' handler._failed = True handler._error_detail = traceback.format_exc() _, _, exc_traceback = sys.exc_info() filename, line_number, func, txt = traceback.extract_tb(exc_traceback)[-1] basename = os.path.basename(filename) handler._error = f"{e}\nFile {basename!r}, line {line_number}, in {func}:\n{txt}" #----------------------------------------------------------------------------- # Private API #----------------------------------------------------------------------------- #----------------------------------------------------------------------------- # Code #-----------------------------------------------------------------------------