Closes #13203: add a FAQ section about seemingly duplicate id()s.
diff --git a/Doc/faq/programming.rst b/Doc/faq/programming.rst
index 3878006..54dc4b9 100644
--- a/Doc/faq/programming.rst
+++ b/Doc/faq/programming.rst
@@ -1724,6 +1724,32 @@
keeping a list of weak references to each instance.
+Why does the result of ``id()`` appear to be not unique?
+--------------------------------------------------------
+
+The :func:`id` builtin returns an integer that is guaranteed to be unique during
+the lifetime of the object. Since in CPython, this is the object's memory
+address, it happens frequently that after an object is deleted from memory, the
+next freshly created object is allocated at the same position in memory. This
+is illustrated by this example:
+
+>>> id(1000)
+13901272
+>>> id(2000)
+13901272
+
+The two ids belong to different integer objects that are created before, and
+deleted immediately after execution of the ``id()`` call. To be sure that
+objects whose id you want to examine are still alive, create another reference
+to the object:
+
+>>> a = 1000; b = 2000
+>>> id(a)
+13901272
+>>> id(b)
+13891296
+
+
Modules
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