gh-141004: Document Py_ARRAY_LENGTH (GH-141601)

Yashp002 · StanFromIreland · picnixz · web-flow · commit e0773eacb7e6 · 2025-11-24T13:34:37.000Z
Co-authored-by: Stan Ulbrych &lt;89152624+StanFromIreland@users.noreply.github.com&gt;
Co-authored-by: Bénédikt Tran &lt;10796600+picnixz@users.noreply.github.com&gt;
Co-authored-by: Peter Bierma &lt;zintensitydev@gmail.com&gt;
diff --git a/Doc/c-api/intro.rst b/Doc/c-api/intro.rst
@@ -322,6 +322,19 @@ complete listing.
       PyDoc_VAR(python_doc) = PyDoc_STR("A genus of constricting snakes in the Pythonidae family native "
                                         "to the tropics and subtropics of the Eastern Hemisphere.");
 
+.. c:macro:: Py_ARRAY_LENGTH(array)
+
+   Compute the length of a statically allocated C array at compile time.
+
+   The *array* argument must be a C array with a size known at compile time.
+   Passing an array with an unknown size, such as a heap-allocated array,
+   will result in a compilation error on some compilers, or otherwise produce
+   incorrect results.
+
+   This is roughly equivalent to::
+
+      sizeof(array) / sizeof((array)[0])
+
 
 .. _api-objects:
 
