Python offers filtering expressions in its generator syntax. I find Python's "lambda" hurts readability for most uses, which pains me as a Lisp geek. Your example, as a generator:

    halve_evens_only = (i / 2) for i in nums if (i%2 == 0)

The parens aren't necessary, but they help readability for people who aren't used to the generator order of operations. (Again, Lisp geek, more parens means more readable in my fractured mind.)