Add an extra hook for locating and loading stateless apps (#168)

* Add an extra hook for locating and loading stateless apps

* Fix typo in test

* Update prerelease version number

* Update test for dash app sideloading

Author: delsim

demo/demo/scaffold.py

@@ -0,0 +1,12 @@
+'Test harness code'
+
+from django_plotly_dash import DjangoDash
+from django.utils.module_loading import import_string
+
+def stateless_app_loader(app_name):
+
+    # Load a stateless app
+    return import_string("demo.scaffold." + app_name)
+
+demo_app = DjangoDash(name="name_of_demo_app")
+

demo/demo/settings.py

@@ -141,6 +141,8 @@
     "cache_arguments" : True, # True for cache, False for session-based argument propagation
 
     #"serve_locally" : True, # True to serve assets locally, False to use their unadulterated urls (eg a CDN)
+
+    "stateless_loader" : "demo.scaffold.stateless_app_loader",
     }
 
 # Static files (CSS, JavaScript, Images)

demo/demo/tests/test_demo_app.py

@@ -87,3 +87,18 @@ def test_app_callbacks():
     assert liveOut
 
     # TODO need something to trigger callbacks
+
+def test_stateless_lookup():
+    'Test side loading of stateless apps'
+
+    from django_plotly_dash.util import stateless_app_lookup_hook
+    lh_hook = stateless_app_lookup_hook()
+
+    with pytest.raises(ImportError):
+        lh_hook("not a real app name")
+
+    demo_app = lh_hook('demo_app')
+
+    assert demo_app is not None
+    assert demo_app._uid == 'name_of_demo_app'
+

django_plotly_dash/dash_wrapper.py

@@ -41,11 +41,14 @@
 
 from .util import static_asset_path
 from .util import serve_locally as serve_locally_setting
+from .util import stateless_app_lookup_hook
 
 uid_counter = 0
 
 usable_apps = {}
 
+_stateless_app_lookup_func = None
+
 def add_usable_app(name, app):
     'Add app to local registry by name'
     name = slugify(name)
@@ -62,12 +65,24 @@ def get_local_stateless_by_name(name):
     Locate a registered dash app by name, and return a DjangoDash instance encapsulating the app.
     '''
     name = slugify(name)
-    # TODO wrap this in raising a 404 if not found
-    try:
-        return usable_apps[name]
-    except:
+
+    sa = usable_apps.get(name, None)
+
+    if not sa:
+
+        global _stateless_app_lookup_func # pylint: disable=global-statement
+
+        if _stateless_app_lookup_func is None:
+            _stateless_app_lookup_func = stateless_app_lookup_hook()
+
+        sa = stateless_app_lookup_func(name)
+
+    if not sa:
+        # TODO wrap this in raising a 404 if not found
         raise KeyError("Unable to find stateless DjangoApp called %s"%name)
 
+    return sa
+
 class Holder:
     'Helper class for holding configuration options'
     def __init__(self):

django_plotly_dash/tests.py

@@ -253,6 +253,16 @@ def test_argument_settings(settings, client):
     assert store_initial_arguments(client, None) is None
     assert get_initial_arguments(client, None) is None
 
+def test_stateless_lookup_noop():
+    'Test no-op stateless lookup'
+
+    from django_plotly_dash.util import stateless_app_lookup_hook
+    lh_hook = stateless_app_lookup_hook()
+
+    assert lh_hook is not None
+    with pytest.raises(ImportError):
+        lh_hook("not an app")
+
 def test_middleware_artifacts():
     'Import and vaguely exercise middleware objects'
 

django_plotly_dash/util.py

@@ -27,6 +27,7 @@
 
 from django.conf import settings
 from django.core.cache import cache
+from django.utils.module_loading import import_string
 
 def _get_settings():
     try:
@@ -117,3 +118,14 @@ def static_path(relative_path):
     except:
         static_url = '/static/'
     return "%s%s" %(static_url, relative_path)
+
+def stateless_app_lookup_hook():
+    'Return a function that performs lookup for aa stateless app, given its name, or returns None'
+
+    func_name = _get_settings().get('stateless_loader', None)
+    if func_name:
+        func = import_string(func_name)
+        return func
+
+    # Default is no additional lookup
+    return lambda _: None

django_plotly_dash/version.py

@@ -23,4 +23,4 @@
 
 '''
 
-__version__ = "0.9.13"
+__version__ = "0.9.14"