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Re:Zed finishes Learn Python The Hard Way by jerf on Wednesday September 29, 2010 @10:55AM (#1739605)
He didn't cover defining first-class functions that I could see in a quick check, didn't cover generators, and I think most disappointingly, didn't cover __metaclass__. That's some critical stuff for Python programming right there, everybody needs __metaclass__.

Ahem.

You have to pick what to cover. For a beginning Python book, I'm underwhelmed by the need to drag an entirely new and foreign(-to-Python) paradigm into the beginning Python. I say this as someone who does a lot of functional programming, someone who is using a lot of lambda, filter, map, and reduce is someone who is stubbornly refusing to program with the native idioms, which are named functions (defined inline is fine), list comprehension or loop, list comprehension or loop, and loop respectively. It is not that enormous a gain, and will lose from Python fighting you all the way. (Plus you'll probably miss some opportunities to use generators, overload the special methods, and the other things you can do with native idioms, if you're trying to program Haskell in Python.)

Re:Zed finishes Learn Python The Hard Way by sharms on Wednesday September 29, 2010 @11:11AM (#1739676)
I have programmed literally hundreds of thousands of lines of python without using classes or __metaclass__, as a counter example.

When dealing in industry, we can't always hire the best talent, so there is no need to make things overly complex. Simple solutions work best for a lot of scenarios, and I haven't been limited by it yet.

Not to bash Perl, but the whole reason we write in Python is because there were too many people on our team writing in Perl using too many obscure constructs that took too long to review / revise (especially years later when team members changed and code was forgotten in parts)

Re:Zed finishes Learn Python The Hard Way by charlief on Wednesday September 29, 2010 @11:35AM (#1739767)
jerf was being sarcastic and transitioned to his point with "Ahem". Let us all celebrate the ambiguity of text.
Re:Zed finishes Learn Python The Hard Way by sigzero on Wednesday September 29, 2010 @11:33AM (#1739762)
Don't blame Perl. Blame the programmers and your methodology that allowed them to do that.
Re:Zed finishes Learn Python The Hard Way by chromatic on Wednesday September 29, 2010 @12:17PM (#1739964)
You can always delay fixing a social problem by switching technologies.
Re:Zed finishes Learn Python The Hard Way by jacobolus on Wednesday September 29, 2010 @09:03PM (#1741840)
You’re implying that language syntax is primarily technical rather than social. I’m not sure I can agree. The reason that Python code uses standard idioms most places you go is that the larger-scale Python community is committed to quite a different set of social norms than the Perl community.

Pulling in that language-community momentum can definitely make a difference to the social/technical dynamics inside a smaller group.

Re:Zed finishes Learn Python The Hard Way by chromatic on Wednesday September 29, 2010 @11:05PM (#1742117)
You’re implying that...

... if you have multiple developers who cannot or will not find some way to write maintainable code, you have a problem independent of language.

I've maintained some hideous code written by people who had no business being professional programmers. In every case, adhering to a handful of very simple rules would have improved their code dramatically. Only one case needed a language change, and that one was away from a proprietary 4GL.

Re:Zed finishes Learn Python The Hard Way by mkramlich on Wednesday September 29, 2010 @09:50PM (#1741947)
Perl is a methodology. ;)
Re:Zed finishes Learn Python The Hard Way by jacobolus on Wednesday September 29, 2010 @08:59PM (#1741834)
Keep in mind too that the new class decorators can do a lot of what metaclasses were good for, in a way much easier for the uninitiated to figure out. (Partly because once you understand function decorators class decorators seem obvious and straightforward.)

Metaclasses can do some pretty powerful stuff though. One of those features that you might never need, but if you do, you really do.

Re:Zed finishes Learn Python The Hard Way by dchest on Wednesday September 29, 2010 @11:15AM (#1739689)
Ahem.
Re:Zed finishes Learn Python The Hard Way by yummyfajitas on Wednesday September 29, 2010 @11:40AM (#1739801)
As far as I know, this piece of code (containing a lambda, map and filter) is standard idiomatic python:

    [ (student.name, 'A') for student in students if student.grade > 90]
I'd assert that first class functions are idiomatic python as well and are also critical for python programming. They play an integral part of django, for example.
Re:Zed finishes Learn Python The Hard Way by jerf on Wednesday September 29, 2010 @12:59PM (#1740112)
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.

Re:Zed finishes Learn Python The Hard Way by shin_lao on Wednesday September 29, 2010 @12:11PM (#1739944)
I thought the book was to be an introduction to programming through Python, that's a good opportunity to show "by the way, you can also see things the functional way...".

I'm no Python expert, I couldn't say what's idiomatic or not. That being said, I never had the feeling of struggling with the language when using map and filter, quite the contrary.

What's the idiomatic way of doing this?

   suffix_str_lst = map(lambda x: x + "_suffix", str_lst)
Re:Zed finishes Learn Python The Hard Way by koenigdavidmj on Wednesday September 29, 2010 @12:20PM (#1739969)
Probably to use a list comprehension:

    suffix_str_lst = [x + "_suffix" for x in str_lst]
If you are okay with a generator instead of a list, then you can flip the square brackets to parentheses and then you do not need to hold the whole thing in memory at once.

EDIT: You can add a filter in a similar way:

    suffix_str_list = [x for x in str_list if x.startswith("meep")]
Re:Zed finishes Learn Python The Hard Way by RyanMcGreal on Wednesday September 29, 2010 @12:52PM (#1740081)
You can also combine maps and filters in a list comprehension:

    suffix_str_lst = ['{0}_suffix'.format(x) for x in str_list if x[:4] == 'meep']
Re:Zed finishes Learn Python The Hard Way by zedshaw on Wednesday September 29, 2010 @01:54PM (#1740348)
Read that out loud and tell me that doesn't grate on your ears? That's my basic test if code for the book would be understood by the reader. What you have here, this "symbol soup" is what makes programming hard for people in the beginning.
Re:Zed finishes Learn Python The Hard Way by angusgr on Wednesday September 29, 2010 @07:48PM (#1741639)
Some of the simpler list comprehensions (like the student one two parents up) are fairly "symbol soup" free, though - and a very clean way of expressing what you want.

OTOH, I can see how they could still be a hard concept for a beginner who hasn't done any functional programming before, particularly because they don't read front-to-back like most imperative statements.

EDIT: You can always split complex ones up as well, for most common usages:

  meeps = [ s for s in str_list if s[:4] == 'meep' ]
  suffix_str_lst = ['{0}_suffix'.format(m) for m in meeps ]
This one was probably a bit simple to really need that, but it's a bit easier to read. :).
Re:Zed finishes Learn Python The Hard Way by RyanMcGreal on Wednesday September 29, 2010 @02:19PM (#1740471)
I actually find it really elegant. I fell in love with comprehensions as soon as I discovered them. They were the terse, expressive syntax I'd long been searching for.
Re:Zed finishes Learn Python The Hard Way by bryanh on Wednesday September 29, 2010 @02:35PM (#1740550)
Is there a tutorial on learning simple one liners like this? I find myself frustrated after seeing simple and obvious solutions like the above, but can never bring myself to code them as such.
Re:Zed finishes Learn Python The Hard Way by steveklabnik on Wednesday September 29, 2010 @03:18PM (#1740717)
http://learnyouahaskell.com

I'm only half kidding. The best way to get used to using functional concepts is to actually use them in their native setting, and then apply (giggle) them elsewhere. When you _have_ to solve problems this way, at some point, it clicks.

Re:Zed finishes Learn Python The Hard Way by mcbain on Wednesday September 29, 2010 @09:52PM (#1741956)
I did something similar to learn a bit of Haskell (to knock the rust off my C geared brain) by picking through a bunch of the problems in http://www.haskell.org/haskellwiki/H-99:_Ninety-Nine_Haskell...

I can say that it has indeed improved my Python scripting as well.