On Tue, 20 Oct 2009 07:39:44 pm Masklinn wrote:
On 20 Oct 2009, at 01:06 , Steven D'Aprano wrote:
If your "anonymous code block" is more complicated than a single short expression, it's too complicated to be "obviously correct" just from looking at it, and so it should be documented and tested.
I have the same issue with this as with Oleg's pronouncement (which runs along the same lines): does that mean you never write for or if statements with more than a single line in them?
No, you are correct, my statement is overly strong. Please insert "very likely" between "it's" and "too complicated".
Yet these are also "anonymous code blocks" which you say here are "too complicated to be obviously correct just from looking at [them]".
If that's the case, why should compound statements even be allowed? They're breeding grounds for multiline anonymous blocks of code…
There is at least one difference between compound statements and multi-statement anonymous code blocks: You don't pass compound statements around as input to other functions, so you know the environment that they're being called in, and can more easily reason about their correctness. But even then, compound statements are good candidates for being converted into named functions too. I usually start with something like this: if cond: do this do that do something else fe fi fo fum ... else: one fish two fish red fish blue fish ... and by the time I'm finished I've got something like this: if cond: call_one() else: call_two() The multi-line blocks are split into functions, each with their own documentation and tests. Of course I don't do this literally every single time. There's no hard rule about how many lines are allowed, just like there's no hard rule about how complex a data structure can be before you give it a name. But my point is that the restriction on lambda is not an odious one, or at least not so odious that it deserves the amount of heat that it generates. There are uses for multi-statement anonymous functions, but there is nothing that an anonymous function can do that a named function can't.[1] In my opinion, it simply isn't enough of a burden to define a function before you use it, using a "don't care" name, to deserve the amount of words written about potential multi-statement lambda syntax. If Python had different syntax, then perhaps we'd have anonymous functions like Ruby. But we don't, and frankly I don't think it is much of a restriction. [1] Some way to write an anonymous code block, which isn't a function and simply runs in the local environment where it is called as if it were written in-line, would be more interesting to me. -- Steven D'Aprano