>>> let = lambda x: 2*x

>>> print let(4)

8

Edit: Awesome, downvoted for helping.

That's not what they mean. The usage they are discussing is more like this, I believe. In a functional context, instead of doing:

    print expensive_computation(), expensive_computation()

You can do:

    (lambda x: print x, x)(expensive_computation())

Which would be equivalent to, with an imaginary let syntax:

    (let x be expensive_computation(): print x, x)