Add construction of callback context variables (#254)

* Add construction of callback context variables

* Only add callback context for extended callbacks

* Add setting of dash global variable

* Add access and reporting of callback context in demo app

* Update test

* Add docs for callback_context

* Add request to documentation of extended callbacks

Co-authored-by: Mark Gibbs <mark@gibbs.consulting>

demo/demo/plotly_apps.py

@@ -342,7 +342,7 @@ def callback_show_timeseries(internal_state_string, state_uid, **kwargs):
      dash.dependencies.Input('dropdown-color', 'value'),
      ])
 def multiple_callbacks_one(button_clicks, color_choice):
-    return ("Output 1: %s %s" % (button_clicks, color_choice),
+    return ("Output 1: %s %s %s" % (button_clicks, color_choice, dash.callback_context.triggered),
             "Output 2: %s %s" % (color_choice, button_clicks),
             "Output 3: %s %s" % (button_clicks, color_choice),
             )
@@ -373,7 +373,7 @@ def multiple_callbacks_one(button_clicks, color_choice):
 def multiple_callbacks_two(button_clicks, color_choice, **kwargs):
     if color_choice == 'green':
         raise PreventUpdate
-    return ["Output 1: %s %s" % (button_clicks, color_choice),
-            "Output 2: %s %s" % (button_clicks, color_choice),
+    return ["Output 1: %s %s %s" % (button_clicks, color_choice, dash.callback_context.triggered),
+            "Output 2: %s %s %s" % (button_clicks, color_choice, kwargs['callback_context'].triggered),
             "Output 3: %s %s [%s]" % (button_clicks, color_choice, kwargs)
             ]

dev_requirements.txt

@@ -19,6 +19,7 @@ pytz
 redis
 sphinx
 sphinx-autobuild
+sphinx_rtd_theme
 twine
 whitenoise
 

django_plotly_dash/dash_wrapper.py

@@ -28,8 +28,10 @@
 import json
 import inspect
 
+import dash
 from dash import Dash
-from dash._utils import split_callback_id
+from dash._utils import split_callback_id, inputs_to_dict
+
 from flask import Flask
 
 from django.urls import reverse
@@ -44,6 +46,54 @@
 from .util import serve_locally as serve_locally_setting
 from .util import stateless_app_lookup_hook
 
+try:
+    from dataclasses import dataclass
+    from typing import Dict, List
+
+    @dataclass(frozen-True)
+    class CallbackContext:
+        inputs_list : List
+        inputs: Dict
+        states_list: List
+        states: Dict
+        outputs_list: List
+        outputs: Dict
+        triggered: List
+
+except:
+    # Not got python 3.7 or dataclasses yet
+    class CallbackContext:
+        def __init__(self, **kwargs):
+            self._args = kwargs
+
+        @property
+        def inputs_list(self):
+            return self._args['inputs_list']
+
+        @property
+        def inputs(self):
+            return self._args['inputs']
+
+        @property
+        def states_list(self):
+            return self._args['states_list']
+
+        @property
+        def states(self):
+            return self._args['states']
+
+        @property
+        def outputs(self):
+            return self._args['outputs']
+
+        @property
+        def outputs_list(self):
+            return self._args['outputs_list']
+        @property
+        def triggered(self):
+            return self._args['triggered']
+
+
 uid_counter = 0
 
 usable_apps = {}
@@ -89,6 +139,7 @@ def get_local_stateless_by_name(name):
 
     return sa
 
+
 class Holder:
     'Helper class for holding configuration options'
     def __init__(self):
@@ -100,6 +151,7 @@ def append_script(self, script):
         'Add extra script file name to component package'
         self.items.append(script)
 
+
 class DjangoDash:
     '''
     Wrapper class that provides Dash functionality in a form that can be served by Django
@@ -511,8 +563,31 @@ def dispatch(self):
     def dispatch_with_args(self, body, argMap):
         'Perform callback dispatching, with enhanced arguments and recording of response'
         inputs = body.get('inputs', [])
-        state = body.get('state', [])
+        input_values = inputs_to_dict(inputs)
+        states = body.get('state', [])
         output = body['output']
+        outputs_list = body.get('outputs') or split_callback_id(output)
+        changed_props = body.get('changedPropIds', [])
+        triggered_inputs = [{"prop_id": x, "value": input_values.get(x)} for x in changed_props]
+
+        callback_context_info = {
+            'inputs_list': inputs,
+            'inputs': input_values,
+            'states_list': states,
+            'states': inputs_to_dict(states),
+            'outputs_list': outputs_list,
+            'outputs': outputs_list,
+            'triggered': triggered_inputs,
+            }
+
+        callback_context = CallbackContext(**callback_context_info)
+
+        # Overload dash global variable
+        dash.callback_context = callback_context
+
+        # Add context to arg map, if extended callbacks in use
+        if len(argMap) > 0:
+            argMap['callback_context'] = callback_context
 
         outputs = []
         try:

django_plotly_dash/tests.py

@@ -198,7 +198,7 @@ def test_injection_updating_multiple_callbacks(client):
         resp_detail = resp['response']
         assert 'output-two' in resp_detail
         assert 'children' in resp_detail['output-two']
-        assert resp_detail['output-two']['children'] == "Output 2: 10 purple-ish yellow with a hint of greeny orange"
+        assert resp_detail['output-two']['children'] == "Output 2: 10 purple-ish yellow with a hint of greeny orange []"
 
 
 @pytest.mark.django_db

docs/extended_callbacks.rst

@@ -39,16 +39,27 @@ For example, the ``plotly_apps.py`` example contains this dash application:
 
 The additional arguments, which are reported as the ``kwargs`` content in this example, include
 
+:callback_context: The ``Dash`` callback context. See the `documentation <https://dash.plotly.com/advanced-callbacks`_ on the content of
+                   this variable. This variable is provided as an argument to the expanded callback as well as
+                   the ``dash.callback_context`` global variable.
 :dash_app: For stateful applications, the ``DashApp`` model instance
 :dash_app_id: The application identifier. For stateless applications, this is the (slugified) name given to the ``DjangoDash`` constructor.
               For stateful applications, it is the (slugified) unique identifier for the associated model instance.
+:request: The Django request object.
 :session_state: A dictionary of information, unique to this user session. Any changes made to its content during the
                 callback are persisted as part of the Django session framework.
 :user: The Django User instance.
 
 The ``DashApp`` model instance can also be configured to persist itself on any change. This is discussed
 in the :ref:`models_and_state` section.
 
+The ``callback_context`` argument is provided in addition to the ``dash.callback_context`` global variable. As a rule, the use of
+global variables should generally be avoided. The context provided by ``django-plotly-dash`` is not the same as the one
+provided by the underlying ``Dash`` library, although its property values are the same and code that uses the content of this
+variable should work unchanged. The use of
+this global variable in any asychronous or multithreaded application is not
+supported, and the use of the callback argument is strongly recommended for all use cases.
+
 
 .. _using_session_state:
 Using session state