Source code for bokeh.application.handlers.handler
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# Copyright (c) 2012 - 2019, 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 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):
''' 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
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# Private API
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# Code
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