Merge pull request #3626 from plotly/fix-global-backend

remove global backends.backend

Author: T4rk1n

dash/_callback.py

@@ -20,7 +20,7 @@
     BackgroundCallbackError,
     ImportedInsideCallbackError,
 )
-
+from ._get_app import get_app
 from ._grouping import (
     flatten_grouping,
     make_grouping_by_index,
@@ -39,7 +39,6 @@
 from ._callback_context import context_value
 from ._no_update import NoUpdate
 from . import _validate
-from . import backends
 
 
 async def _async_invoke_callback(
@@ -373,7 +372,7 @@ def _get_callback_manager(
                 " and store results on redis.\n"
             )
 
-    adapter = backends.backend.request_adapter()
+    adapter = get_app().backend.request_adapter()
     old_job = adapter.args.getlist("oldJob") if hasattr(adapter.args, "getlist") else []
 
     if old_job:
@@ -433,7 +432,7 @@ def _setup_background_callback(
 
 def _progress_background_callback(response, callback_manager, background):
     progress_outputs = background.get("progress")
-    adapter = backends.backend.request_adapter()
+    adapter = get_app().backend.request_adapter()
     cache_key = adapter.args.get("cacheKey")
 
     if progress_outputs:
@@ -451,7 +450,7 @@ def _update_background_callback(
     """Set up the background callback and manage jobs."""
     callback_manager = _get_callback_manager(kwargs, background)
 
-    adapter = backends.backend.request_adapter()
+    adapter = get_app().backend.request_adapter()
     cache_key = adapter.args.get("cacheKey") if adapter else None
     job_id = adapter.args.get("job") if adapter else None
 
@@ -473,7 +472,7 @@ def _handle_rest_background_callback(
     multi,
     has_update=False,
 ):
-    adapter = backends.backend.request_adapter()
+    adapter = get_app().backend.request_adapter()
     cache_key = adapter.args.get("cacheKey") if adapter else None
     job_id = adapter.args.get("job") if adapter else None
     # Must get job_running after get_result since get_results terminates it.
@@ -691,7 +690,7 @@ def add_context(*args, **kwargs):
             jsonResponse: Optional[str] = None
             try:
                 if background is not None:
-                    adapter = backends.backend.request_adapter()
+                    adapter = get_app().backend.request_adapter()
                     if not (adapter and adapter.args.get("cacheKey")):
                         return _setup_background_callback(
                             kwargs,
@@ -763,7 +762,7 @@ async def async_add_context(*args, **kwargs):
 
             try:
                 if background is not None:
-                    adapter = backends.backend.request_adapter()
+                    adapter = get_app().backend.request_adapter()
                     if not (adapter and adapter.args.get("cacheKey")):
                         return _setup_background_callback(
                             kwargs,

dash/_callback_context.py

@@ -5,7 +5,7 @@
 import typing
 
 from . import exceptions
-from . import backends
+from ._get_app import get_app
 from ._utils import AttributeDict, stringify_id
 
 
@@ -221,7 +221,7 @@ def record_timing(name, duration, description=None):
         :param description: A description of the resource.
         :type description: string or None
         """
-        request = backends.backend.request_adapter()
+        request = get_app().backend.request_adapter()
         timing_information = getattr(request.context, "timing_information", {})
 
         if name in timing_information:
@@ -252,7 +252,7 @@ def using_outputs_grouping(self):
     @property
     @has_context
     def timing_information(self):
-        request = backends.backend.request_adapter()
+        request = get_app().backend.request_adapter()
         return getattr(request.context, "timing_information", {})
 
     @has_context

dash/_get_app.py

@@ -4,6 +4,8 @@
 from textwrap import dedent
 from typing import Any, Optional
 
+from dash.exceptions import AppNotFoundError
+
 APP: Optional[Any] = None
 
 app_context: ContextVar[Any] = ContextVar("dash_app_context")
@@ -55,7 +57,7 @@ def get_app():
         pass
 
     if APP is None:
-        raise Exception(
+        raise AppNotFoundError(
             dedent(
                 """
                 App object is not yet defined.  `app = dash.Dash()` needs to be run

dash/_validate.py

@@ -9,6 +9,7 @@
 from .development.base_component import Component
 from . import backends
 from . import exceptions
+from ._get_app import get_app
 from ._utils import (
     patch_collections_abc,
     stringify_id,
@@ -510,13 +511,17 @@ def validate_use_pages(config):
             "`dash.register_page()` must be called after app instantiation"
         )
 
-    if backends.backend.has_request_context():
-        raise exceptions.PageError(
-            """
-            dash.register_page() can’t be called within a callback as it updates dash.page_registry, which is a global variable.
-             For more details, see https://dash.plotly.com/sharing-data-between-callbacks#why-global-variables-will-break-your-app
-            """
-        )
+    try:
+        if get_app().backend.has_request_context():
+            raise exceptions.PageError(
+                """
+                dash.register_page() can’t be called within a callback as it updates dash.page_registry, which is a global variable.
+                For more details, see https://dash.plotly.com/sharing-data-between-callbacks#why-global-variables-will-break-your-app
+                """
+            )
+    except exceptions.AppNotFoundError:
+        # If the app is not found we can add pages since before instantiation.
+        pass
 
 
 def validate_module_name(module):

dash/backends/__init__.py

@@ -4,9 +4,6 @@
 from .base_server import BaseDashServer
 
 
-backend: BaseDashServer
-
-
 _backend_imports = {
     "flask": ("dash.backends._flask", "FlaskDashServer"),
     "fastapi": ("dash.backends._fastapi", "FastAPIDashServer"),
@@ -74,6 +71,5 @@ def get_server_type(server):
 
 __all__ = [
     "get_backend",
-    "backend",
     "get_server_type",
 ]

dash/dash.py

@@ -501,14 +501,10 @@ def __init__(  # pylint: disable=too-many-statements, too-many-branches
 
             self.backend = backend_cls(server)
             self.server = server
-            backends.backend = self.backend  # type: ignore
-            backends.request_adapter = self.backend.request_adapter  # type: ignore
         else:
             # No server instance provided, create backend and let backend create server
             self.server = backend_cls.create_app(caller_name)  # type: ignore
             self.backend = backend_cls(self.server)
-            backends.backend = self.backend
-            backends.request_adapter = self.backend.request_adapter  # type: ignore
 
         base_prefix, routes_prefix, requests_prefix = pathname_configs(
             url_base_pathname, routes_pathname_prefix, requests_pathname_prefix
@@ -641,6 +637,7 @@ def __init__(  # pylint: disable=too-many-statements, too-many-branches
         self._got_first_request = {"pages": False, "setup_server": False}
 
         if server:
+            print(f"init app from server {server}")
             self.init_app()
 
         self.logger.setLevel(logging.INFO)
@@ -1179,7 +1176,7 @@ def index(self, *_args, **_kwargs):
         renderer = self._generate_renderer()
         title = self.title
         # Refactored: direct access to global request adapter
-        request = backends.backend.request_adapter()
+        request = self.backend.request_adapter()
 
         if self.use_pages and self.config.include_pages_meta and request:
             metas = _page_meta_tags(self, request) + metas
@@ -1395,7 +1392,7 @@ def _inputs_to_vals(self, inputs):
     # pylint: disable=R0915
     def _initialize_context(self, body):
         """Initialize the global context for the request."""
-        adapter = backends.backend.request_adapter()
+        adapter = self.backend.request_adapter()
         g = AttributeDict({})
         g.inputs_list = body.get("inputs", [])
         g.states_list = body.get("state", [])
@@ -2382,7 +2379,7 @@ def verify_url_part(served_part, url_part, part_name):
                 server_url=jupyter_server_url,
             )
         else:
-            backends.backend.run(
+            self.backend.run(
                 dash_app=self, host=host, port=port, debug=debug, **flask_run_options
             )
 

dash/exceptions.py

@@ -109,3 +109,7 @@ class ImportedInsideCallbackError(DashException):
 
 class HookError(DashException):
     pass
+
+
+class AppNotFoundError(DashException):
+    pass