simplify creation of transparent legend

Author: esc

doc/users/recipes.rst

@@ -330,8 +330,7 @@ nice to make the legend frame transparent.
    ax.plot(np.random.randn(300), 'o-', label='normal distribution')
    ax.plot(np.random.rand(300), 's-', label='uniform distribution')
    ax.set_ylim(-3, 3)
-   leg = ax.legend(loc='best', fancybox=True)
-   leg.get_frame().set_alpha(0.5)
+   ax.legend(loc='best', fancybox=True, framealpha=0.5)
 
    ax.set_title('fancy, transparent legends')