[extractor] Import `_ALL_CLASSES` lazily

This significantly speeds up `import yt_dlp` in the absence of `lazy_extractors`

1 files changed, 4 insertions, 1 deletions

diff --git a/yt_dlp/compat/compat_utils.py b/yt_dlp/compat/compat_utils.py
index b1d58f5b9..8da4fcc0a 100644
--- a/yt_dlp/compat/compat_utils.py
+++ b/yt_dlp/compat/compat_utils.py
@@ -33,7 +33,7 @@ def _is_package(module):
 
 def passthrough_module(parent, child, *, callback=lambda _: None):
     parent_module = importlib.import_module(parent)
-    child_module = importlib.import_module(child, parent)
+    child_module = None  # Import child module only as needed
 
     class PassthroughModule(types.ModuleType):
         def __getattr__(self, attr):
@@ -41,6 +41,9 @@ def passthrough_module(parent, child, *, callback=lambda _: None):
                 with contextlib.suppress(ImportError):
                     return importlib.import_module(f'.{attr}', parent)
 
+            nonlocal child_module
+            child_module = child_module or importlib.import_module(child, parent)
+
             ret = _NO_ATTRIBUTE
             with contextlib.suppress(AttributeError):
                 ret = getattr(child_module, attr)