On Mon, 24 Mar 2014 22:49:38 +1100, Chris Angelico wrote: > On Mon, Mar 24, 2014 at 8:55 PM, Marko Rauhamaa <ma...@pacujo.net> > wrote:
>> You never *need* (Python's) lambda for anything. Inner functions are >> more capable and almost always more readable. It doesn't hurt to have >> lambda, but I don't find any use for it, either. Marko has missed an obvious use: lambda is the *only* solution when you need a function embedded in an expression. You simply cannot do so otherwise. It is truly astonishing that two people here who are such keen supporters of functional programming, Marko and Mark Harris, are so dismissive of lambda, and so forced to write declarative code using def. > They're often not more readable. A lot of people seem to equate > "verbose" with "readable", possibly by faulty extrapolation from > unreadably crunched code with one-letter variables and no line breaks. > But which of these is truly more readable? > > squares = [] > for n in range(30): > squares.append(n * n) > > squares = [n * n for n in range(30)] Readable for whom? List comprehension syntax is often completely obscure to beginners. A beginner would say that the explicit for-loop is more readable. Actually, a *real* beginner, whose main programming experience before Python was Pascal, would probably even say that the first example was an unreadable mess. What's range(30)? What's this ".append" business? What does [] mean? I know this because I was this beginner, once. The first few times I tried reading Python code, I couldn't make head or tail of it. "for" I recognised, because it was the same keyword as Pascal and Hypertalk use. Pretty much everything else might as well have been Bulgarian. This was before the public internet, there was no Google, no tutorials I could look up. It was only after a colleague convinced me that it would be a good language to learn that I bought an actual dead tree book and sat down and learned how to read Python. I think that Python's reputation of being "executable pseudo-code" is sometimes harmful. It fools people into thinking that unless Aunt Tilly can understand a language feature, it's somehow a failure. Hence the arguments by Mark against lambda. http://www.catb.org/jargon/html/A/Aunt-Tillie.html But nobody expects Aunt Tilly to read Scheme or C++ or Go without at least a bit of learning -- or even Esperanto or French or Latin. You still need to learn the syntax and the vocabulary, and have some idea of the basic concepts. The same applies to Python. The learning curve may be more gentle, but there is still a learning curve. And that is perfectly fine. So while I agree with you that, to a moderately fluent Python speaker, not a beginner but not an expert either, the list comprehension is more readable, for a beginner (one who has a basic Python vocab but isn't fluent yet) the for-loop will probably be more readable. > Similarly, there are plenty of cases where a nameless function is MUCH > clearer than breaking it out into a separate def and then using the name > once. Do you name the function for what it does internally? > > def get_oneth_element_index(item): > return item[1].index > L.sort(key=get_oneth_element_index) > > Or for how you're using it? > > def keyfunc(item): > return item[1].index > L.sort(key=keyfunc) Why not both?! Don't forget to make it private so some other piece of code doesn't use it. Or better still, delete it when done! def _get_oneth_element_index_to_use_as_keyfunc_when_sorting_L(item): return item[1].index L.sort(key=_get_oneth_element_index_to_use_as_keyfunc_when_sorting_L) del _get_oneth_element_index_to_use_as_keyfunc_when_sorting_L Four lines of code to do what lambda lets you do in one. And people still insist that lambda is pointless. Maybe they're being paid by the line. > Or do you just shortcut the whole thing by inlining it? > > L.sort(key=lambda item:item[1].index) Exactly. -- Steven D'Aprano http://import-that.dreamwidth.org/ -- https://mail.python.org/mailman/listinfo/python-list
