[Python-Dev] RE: list comprehensions (was parsers and compilers for 2.0) (original) (raw)

Thomas Wouters thomas@xs4all.net
Mon, 14 Aug 2000 07:57:13 +0200

Well, Tim, thanx for that mini-PEP, if I can call your recap of years of discussion that ;-) It did clear up my mind, though I have a few comments to make. This is the last I have to say about it, though, I didn't intend to drag you into a new long discussion ;)

On Sun, Aug 13, 2000 at 08:08:45PM -0400, Tim Peters wrote:

Guido feels exactly the opposite: the business about "alien, forced feel, not fitting" is exactly what he's said about map/filter/reduce/lambda on many occasions.

Note that I didn't mention lambda, and did so purposely ;) Yes, listcomps are much better than lambda. And I'll grant the special case of 'None' as the function is unpythonic, in map/filter/reduce. Other than that, they're just functions, which I hope aren't too unpythonic

> [((a,b)*c, (spam(d)%34)^e) for a in [(x, y) for x in L for y in > S] for b in [b for b in B if mean(b)] for b,c in C for a,d in D > for e in [Egg(a, b, c, d, e) for e in E]]

That isn't a serious argument, to my eyes.

Well, it's at the core of my doubts :) 'for' and 'if' start out of thin air. I don't think any other python statement or expression can be repeated and glued together without any kind of separator, except string literals (which I can see the point of, but scared me a little none the less.)

I don't know enough lisp to write this expression in that, but I assume you could still match the parentheses to find out how they are grouped.

I know you missed that possibility above because, despite your claim of being hard to parse, it's dead easy to spot where your listcomps begin: "[" is easy for the eye to find.

That's the start of a listcomp, but not of a specific listcomp-for or -if.

> I hope anyone writing something like that (notice the shadowing of > some of the outer vrbls in the inner loops)

You can find the same in nested lambdas littering map/reduce/etc today.

Yes, and wasn't the point to remove those ?

Like I said, I'm not arguing against listcomprehensions, I'm just saying I'm sorry we didn't get yet another debate on syntax ;) Having said that, I'll step back and let Eric's predicted doom fall over Python; hopefully we are wrong and you all are right :-)

-- Thomas Wouters <thomas@xs4all.net>

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