With [...] you are doing the same as list(...), so your example would return a list: >>> evens_only([1,2,3,4,5]) [1, 2] If you want a generator instea

With [...] you are doing the same as list(...), so your example would return a list: >>> evens_only([1,2,3,4,5]) [1, 2] If you want a generator instead: evens_only = lambda nums: (n/2 for n in nums if n%2==0) So you'll get: >>> evens_only([1,2,3,4,5]) <generator object <genexpr> at 0x7f2ef79eaa00> I don't know which one would be more Pythonic, clean and simple lambda one-liner or two-lined simple function.