[3.15] gh-148587: Document sys.lazy_modules (GH-150742)

(cherry picked from commit e3fa52d)

Co-authored-by: Bartosz Sławecki <bartosz@ilikepython.com>

Author: miss-islington

Doc/library/sys.rst

@@ -1483,6 +1483,21 @@ always available. Unless explicitly noted otherwise, all variables are read-only
    They hold the legacy representation of ``sys.last_exc``, as returned
    from :func:`exc_info` above.
 
+
+.. data:: lazy_modules
+
+   A :class:`set` of fully qualified module name strings that have been lazily
+   imported in the current interpreter but not yet loaded.  When a
+   lazily imported module is accessed for the first time, its name is removed
+   from this set.
+
+   This attribute is intended for debugging and introspection.
+
+   See also :func:`set_lazy_imports` and :pep:`810`.
+
+   .. versionadded:: 3.15
+
+
 .. data:: maxsize
 
    An integer giving the maximum value a variable of type :c:type:`Py_ssize_t` can

Misc/NEWS.d/3.15.0a8.rst

@@ -350,7 +350,7 @@ Fix :func:`repr` for lists and tuples containing ``NULL``\ s.
 .. nonce: aB3xKm
 .. section: Core and Builtins
 
-Fixed ``sys.lazy_modules`` to include lazy modules without submodules. Patch
+Fixed :py:attr:`sys.lazy_modules` to include lazy modules without submodules. Patch
 by Bartosz Sławecki.
 
 ..

Misc/NEWS.d/3.15.0b2.rst

@@ -132,7 +132,7 @@ function call.
 .. nonce: -RD3z5
 .. section: Core and Builtins
 
-``sys.lazy_modules`` is now a set instead of a dict as initially spelled out
+:py:attr:`sys.lazy_modules` is now a set instead of a dict as initially spelled out
 in PEP 810.
 
 ..