Add separate init_app function for providing the flask app

Author: multimeric

dash/dash.py

@@ -108,8 +108,13 @@ def __init__(
             components_cache_max_age=None,
             show_undo_redo=False,
             plugins=None,
+            defer_app=False,
             **kwargs):
 
+        # Store some flask-related parameters for use in init_app()
+        self.compress = compress
+        self.name = name
+
         # pylint-disable: too-many-instance-attributes
         if 'csrf_protect' in kwargs:
             warnings.warn('''
@@ -154,22 +159,6 @@ def __init__(
             'show_undo_redo': show_undo_redo
         })
 
-        assets_blueprint_name = '{}{}'.format(
-            self.config.routes_pathname_prefix.replace('/', '_'),
-            'dash_assets'
-        )
-
-        self.server.register_blueprint(
-            flask.Blueprint(
-                assets_blueprint_name, name,
-                static_folder=self._assets_folder,
-                static_url_path='{}{}'.format(
-                    self.config.routes_pathname_prefix,
-                    assets_url_path.lstrip('/')
-                )
-            )
-        )
-
         # list of dependencies
         self.callback_map = {}
 
@@ -181,15 +170,6 @@ def __init__(
         # default renderer string
         self.renderer = 'var renderer = new DashRenderer();'
 
-        if compress:
-            # gzip
-            Compress(self.server)
-
-        @self.server.errorhandler(exceptions.PreventUpdate)
-        def _handle_error(_):
-            """Handle a halted callback and return an empty 204 response"""
-            return '', 204
-
         # static files from the packages
         self.css = Css()
         self.scripts = Scripts()
@@ -236,8 +216,6 @@ def _handle_error(_):
             '{}_favicon.ico'.format(prefix),
             self._serve_default_favicon)
 
-        self.server.before_first_request(self._setup_server)
-
         self._layout = None
         self._cached_layout = None
         self._dev_tools = _AttributeDict({
@@ -250,10 +228,6 @@ def _handle_error(_):
             'props_check': False,
         })
 
-        # add a handler for components suites errors to return 404
-        self.server.errorhandler(exceptions.InvalidResourceError)(
-            self._invalid_resources_handler)
-
         self._assets_files = []
 
         # hot reload
@@ -270,6 +244,49 @@ def _handle_error(_):
             for plugin in plugins:
                 plugin.plug(self)
 
+        if not defer_app:
+            self.init_app()
+
+    def init_app(self, app=None):
+        """
+        Initialize the parts of Dash that require a flask app
+        """
+
+        if app is not None:
+            self.server = app
+
+        assets_blueprint_name = '{}{}'.format(
+            self.config.routes_pathname_prefix.replace('/', '_'),
+            'dash_assets'
+        )
+
+        self.server.register_blueprint(
+            flask.Blueprint(
+                assets_blueprint_name,
+                self.name,
+                static_folder=self._assets_folder,
+                static_url_path='{}{}'.format(
+                    self.config.routes_pathname_prefix,
+                    self._assets_url_path.lstrip('/')
+                )
+            )
+        )
+
+        if self.compress:
+            # gzip
+            Compress(self.server)
+
+        @self.server.errorhandler(exceptions.PreventUpdate)
+        def _handle_error(_):
+            """Handle a halted callback and return an empty 204 response"""
+            return '', 204
+
+        self.server.before_first_request(self._setup_server)
+
+        # add a handler for components suites errors to return 404
+        self.server.errorhandler(exceptions.InvalidResourceError)(
+            self._invalid_resources_handler)
+
     def _add_url(self, name, view_func, methods=('GET',)):
         self.server.add_url_rule(
             name,
@@ -404,7 +421,7 @@ def _relative_url_path(relative_package_path='', namespace=''):
                 paths = [paths] if isinstance(paths, str) else paths
 
                 for rel_path in paths:
-                    self.registered_paths[resource['namespace']]\
+                    self.registered_paths[resource['namespace']] \
                         .add(rel_path)
 
                     if not is_dynamic_resource:
@@ -432,7 +449,7 @@ def _relative_url_path(relative_package_path='', namespace=''):
 
     def _generate_css_dist_html(self):
         links = self._external_stylesheets + \
-            self._collect_and_register_resources(self.css.get_all_css())
+                self._collect_and_register_resources(self.css.get_all_css())
 
         return '\n'.join([
             _format_tag('link', link, opened=True)
@@ -454,12 +471,12 @@ def _generate_scripts_html(self):
                 dash_renderer._js_dist_dependencies,
                 dev_bundles=self._dev_tools.serve_dev_bundles
             )) + self._external_scripts + self._collect_and_register_resources(
-                self.scripts.get_all_scripts(
-                    dev_bundles=self._dev_tools.serve_dev_bundles) +
-                self.scripts._resources._filter_resources(
-                    dash_renderer._js_dist,
-                    dev_bundles=self._dev_tools.serve_dev_bundles
-                ))
+            self.scripts.get_all_scripts(
+                dev_bundles=self._dev_tools.serve_dev_bundles) +
+            self.scripts._resources._filter_resources(
+                dash_renderer._js_dist,
+                dev_bundles=self._dev_tools.serve_dev_bundles
+            ))
 
         return '\n'.join([
             _format_tag('script', src)
@@ -509,14 +526,14 @@ def serve_component_suites(self, package_name, path_in_package_dist):
                 'Error loading dependency.\n'
                 '"{}" is not a registered library.\n'
                 'Registered libraries are: {}'
-                .format(package_name, list(self.registered_paths.keys())))
+                    .format(package_name, list(self.registered_paths.keys())))
 
         if path_in_package_dist not in self.registered_paths[package_name]:
             raise exceptions.DependencyException(
                 '"{}" is registered but the path requested is not valid.\n'
                 'The path requested: "{}"\n'
                 'List of registered paths: {}'
-                .format(
+                    .format(
                     package_name,
                     path_in_package_dist,
                     self.registered_paths
@@ -775,7 +792,7 @@ def _validate_callback(self, output, inputs, state):
                             arg.component_property,
                             arg.component_id,
                             component.available_properties).replace(
-                                '    ', ''))
+                            '    ', ''))
 
                     if hasattr(arg, 'component_event'):
                         raise exceptions.NonExistentEventException('''
@@ -871,19 +888,19 @@ def _raise_invalid(bad_val, outer_val, bad_type, path, index=None,
                     or is in the top level of the returned list,'''
                 ),
                 location=(
-                    "\n" +
-                    ("[{:d}] {:s} {:s}".format(index, outer_type, outer_id)
-                     if index is not None
-                     else ('[*] ' + outer_type + ' ' + outer_id))
-                    + "\n" + path + "\n"
+                        "\n" +
+                        ("[{:d}] {:s} {:s}".format(index, outer_type, outer_id)
+                         if index is not None
+                         else ('[*] ' + outer_type + ' ' + outer_id))
+                        + "\n" + path + "\n"
                 ) if not toplevel else '',
                 bad_val=bad_val).replace('    ', ''))
 
         def _value_is_valid(val):
             return (
                 # pylint: disable=unused-variable
-                any([isinstance(val, x) for x in valid]) or
-                type(val).__name__ == 'unicode'
+                    any([isinstance(val, x) for x in valid]) or
+                    type(val).__name__ == 'unicode'
             )
 
         def _validate_value(val, index=None):
@@ -1140,17 +1157,17 @@ def dispatch(self):
 
         for component_registration in self.callback_map[output]['inputs']:
             args.append([
-                c.get('value', None) for c in inputs if
-                c['property'] == component_registration['property'] and
-                c['id'] == component_registration['id']
-            ][0])
+                            c.get('value', None) for c in inputs if
+                            c['property'] == component_registration['property'] and
+                            c['id'] == component_registration['id']
+                        ][0])
 
         for component_registration in self.callback_map[output]['state']:
             args.append([
-                c.get('value', None) for c in state if
-                c['property'] == component_registration['property'] and
-                c['id'] == component_registration['id']
-            ][0])
+                            c.get('value', None) for c in state if
+                            c['property'] == component_registration['property'] and
+                            c['id'] == component_registration['id']
+                        ][0])
 
         response.set_data(self.callback_map[output]['callback'](*args))
         return response