bpo-38558: Mention := in conditions tutorial (GH-16919)

Author: ammaraskar

Doc/tutorial/datastructures.rst

@@ -675,10 +675,10 @@ to a variable.  For example, ::
    >>> non_null
    'Trondheim'
 
-Note that in Python, unlike C, assignment cannot occur inside expressions. C
-programmers may grumble about this, but it avoids a common class of problems
-encountered in C programs: typing ``=`` in an expression when ``==`` was
-intended.
+Note that in Python, unlike C, assignment inside expressions must be done
+explicitly with the walrus operator ``:=``. This avoids a common class of
+problems encountered in C programs: typing ``=`` in an expression when ``==``
+was intended.
 
 
 .. _tut-comparing: