Add mention of swap idiom to 'The Old Switcheroo' exercise

_episodes/08-func.md

@@ -918,6 +918,10 @@ readable code!
 > > `a` and `b` in this case) and trades their values. The function does not
 > > return any values and does not alter `a` or `b` outside of its local copy.
 > > Therefore the original values of `a` and `b` remain unchanged.
+> >
+> > Note that the recommended way of swapping the content of `a` and `b` in Python is
+> > `a, b = b, a`. You can see why this works in the
+> > [Additional Exercises]({{ page.root }}/extra_exercises/index.html).
 > {: .solution}
 {: .challenge}
 

_extras/extra_exercises.md

@@ -22,7 +22,7 @@ or not (yet) added to the main lesson.
 > Compare it to:
 >
 > ~~~
-> left, right = [right, left]
+> left, right = right, left
 > ~~~
 > {: .language-python}
 >
@@ -44,7 +44,8 @@ or not (yet) added to the main lesson.
 > >
 > > In the first case we used a temporary variable `temp` to keep the value of `left` before we
 > > overwrite it with the value of `right`. In the second case, `right` and `left` are packed into a
-> > list and then unpacked into `left` and `right`.
+> > [tuple]({{ page.root }}/reference.html#tuple)
+> > and then unpacked into `left` and `right`.
 > {: .solution}
 {: .challenge}