Change default use_param=None and value of False now disables Pages e…

…ven when pages_folder has custom value

dash/dash.py

@@ -205,9 +205,10 @@ class Dash:
         for pages of a multi-page app. Default ``'pages'``.
     :type pages_folder: string
 
-    :param use_pages:  Default False, or True if you set a non-default ``pages_folder``.
-        When True, the ``pages`` feature for multi-page apps is enabled.
-    :type pages: boolean
+    :param use_pages: When True, the ``pages`` feature for multi-page apps is
+        enabled. If you set a non-default ``pages_folder`` this will be inferred
+        to be True. Default `None`.
+    :type use_pages: boolean
 
     :param assets_url_path: The local urls for assets will be:
         ``requests_pathname_prefix + assets_url_path + '/' + asset_path``
@@ -341,7 +342,7 @@ def __init__(  # pylint: disable=too-many-statements
         server=True,
         assets_folder="assets",
         pages_folder="pages",
-        use_pages=False,
+        use_pages=None,
         assets_url_path="assets",
         assets_ignore="",
         assets_external_path=None,
@@ -439,7 +440,7 @@ def __init__(  # pylint: disable=too-many-statements
         _pages.CONFIG = self.config
 
         self.pages_folder = str(pages_folder)
-        self.use_pages = True if pages_folder != "pages" else use_pages
+        self.use_pages = (pages_folder != "pages") if use_pages is None else use_pages
 
         # keep title as a class property for backwards compatibility
         self.title = title

tests/unit/pages/test_pages_config.py

@@ -65,17 +65,26 @@ def test_pages_missing_path_config(empty_environ, pages_folder, use_pages, expec
 
 
 @pytest.mark.parametrize(
-    "pages_folder",
+    "use_pages, pages_folder",
     [
-        "custom_pages",
-        Path("custom_pages"),
-        str(THIS_DIR / "custom_pages"),
-        THIS_DIR / "custom_pages",
-        str(THIS_DIR / "sub_dir" / "custom_pages"),
-        THIS_DIR / "sub_dir" / "custom_pages",
+        (True, "custom_pages"),
+        (True, Path("custom_pages")),
+        (True, str(THIS_DIR / "custom_pages")),
+        (True, THIS_DIR / "custom_pages"),
+        (True, str(THIS_DIR / "sub_dir" / "custom_pages")),
+        (True, THIS_DIR / "sub_dir" / "custom_pages"),
+        (None, "custom_pages"),
+        (None, "pages"),
+        (False, "custom_pages"),
     ],
 )
-def test_pages_folder_app_config(empty_environ, clear_pages_state, pages_folder):
-    app = Dash(__name__, pages_folder=pages_folder)
-    assert app.use_pages
+def test_pages_folder_app_config(
+    empty_environ, clear_pages_state, use_pages, pages_folder
+):
+    app = Dash(__name__, use_pages=use_pages, pages_folder=pages_folder)
+    if use_pages is None:
+        expected_use_pages = bool(pages_folder != "pages")
+    elif use_pages in (True, False):
+        expected_use_pages = use_pages
+    assert app.use_pages == expected_use_pages
     assert app.pages_folder == str(pages_folder)