PEP 810: Add some clarifications on LazyLoader (#4677)

Author: pablogsal

peps/pep-0810.rst

@@ -1250,11 +1250,29 @@ method.
 Why not use ``importlib.util.LazyLoader`` instead?
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-``LazyLoader`` has significant limitations:
-
-- Requires verbose setup code for each lazy import.
-- Doesn't work well with ``from ... import`` statements.
-- Less clear and standard than dedicated syntax.
+The standard library's :class:`~importlib.util.LazyLoader` was designed for
+specific use cases but has fundamental limitations as a general-purpose lazy
+import mechanism.
+
+Most critically, ``LazyLoader`` does not support ``from ... import`` statements.
+There is no straightforward mechanism to lazily import specific attributes from
+a module - users would need to manually wrap and proxy individual attributes,
+which is both error-prone and defeats the performance benefits.
+
+Additionally, ``LazyLoader`` must resolve the module spec before creating the
+lazy loader, which introduces overhead that reduces the performance benefits of
+lazy loading. The spec resolution involves filesystem operations and path
+searching that this PEP's approach defers until actual module use.
+
+``LazyLoader`` also operates at the import machinery level rather than providing
+language-level syntax, which means there's no canonical way for tools like
+linters and type checkers to recognize lazy imports. A dedicated syntax enables
+ecosystem-wide standardization and allows compiler and runtime optimizations
+that would be impossible with a purely library-based approach.
+
+Finally, ``LazyLoader`` requires significant boilerplate, involving manual
+manipulation of module specs, loaders, and ``sys.modules``, making it impractical
+for common use cases where multiple modules need to be lazily imported.
 
 Will this break tools like ``isort`` or ``black``?
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