Source code for bokeh.application.handlers.handler

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# Copyright (c) 2012 - 2018, Anaconda, Inc. All rights reserved.
#
# Powered by the Bokeh Development Team.
#
# The full license is in the file LICENSE.txt, distributed with this software.
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''' 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):

            # do some data base lookup here to generate 'plot'

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

            # and return it
            return doc

'''

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# Boilerplate
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from __future__ import absolute_import, division, print_function, unicode_literals

import logging
log = logging.getLogger(__name__)

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# Imports
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# Standard library imports

# External imports

# Bokeh imports

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

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# General API
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# Dev API
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[docs]class Handler(object): ''' Provide a mechanism for Bokeh applications to build up new Bokeh Documents. ''' def __init__(self, *args, **kwargs): self._failed = False self._error = None self._error_detail = None self._static = None # Properties -------------------------------------------------------------- @property def error(self): ''' If the handler fails, may contain a related error message. ''' return self._error @property def error_detail(self): ''' If the handler fails, may contain a traceback or other details. ''' return self._error_detail @property def failed(self): ''' ``True`` if the handler failed to modify the doc ''' return self._failed # Public methods ----------------------------------------------------------
[docs] def modify_document(self, doc): ''' 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): ''' 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): ''' 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] def on_session_created(self, session_context): ''' 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] def on_session_destroyed(self, session_context): ''' 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 static_path(self): ''' Return a path to app-specific static resources, if applicable. ''' if self.failed: return None else: return self._static
[docs] def url_path(self): ''' Returs 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
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