Yes, that's the idiomatic way of doing it, when people complain about lack of map, filter, and lambdas, they're usually missing an opportunity to do it more easily with list comprehensions. Note that doing this with list comprehensions is pretty competitive with Haskell on a keystroke-by-keystroke basis; insisting that your lambdas MUST have the word lambda and the filter MUST have the word filter and that maps MUST have the word map is getting caught up in the surface appearance and missing the deeper flows, which actually, IMHO, isn't a very "functional" attitude to have anyhow.
(Functional programming, IMHO, isn't about maps and folds and filters anyhow; what those are are the tools it uses to gain composability. Python uses other tools for that goal; when in Python, you should use those tools. Ultimately, Python is an imperative language and will have all the associated flaws, functional probably does a better job of composability overall. But if you're in Python, you're not going to build a cute monadic combinator library that you can use in Python no matter how hard you try to box it about the ears with map and reduce, so you might as well use what Python actually has, which is classes and generators and list/generator comprehensions and lots of very overloadable syntax and so on and so forth. maps and folds and filters are the surface of functional programming, not the essense.)
(And yes, you can build a combinator library, you just can't make it slick.)
Reduce is the only one that is not clean in Python ("fold"), and the official word is to use loops. Again, it's usually not that great a loss, but the loss vs Haskell is greatest here. On the other hand, compared against some actually-functional languages you're still not typing much more; Erlang's folds are hardly any better than a Python loop, character-per-character.
accum = 0
for i in l:
accum += i
vs
lists:foldl(fun (I, Accum) -> I + Accum end, 0, L)
First class-functions are absolutely idiomatic; what's not idiomatic is smashing things together with crazy "and" or "or" chains (or a variety of other hacky approachs) so you can have the magic-goodness-conferring word "lambda" show up in your source, instead of (
horrors!) having to give your function a name.
Speak the native idioms of the language you are in. A lot of people are missing a lot of the good things about Python because they are too busy complaining that it isn't something that isn't Python. It isn't functional at its core, but it can be a very powerful, concise language, if you work with it instead of fighting it.