Re: Special keyword argument lambda syntax
Beni Cherniavsky beni.cherniav...@gmail.com wrote: This proposal outrageously suggests a special syntax for in-line functions passed as keyword arguments:: sorted(range(9), key(n)=n%3) [0, 3, 6, 1, 4, 7, 2, 5, 8] The claim is that such specialization hits a syntax sweet spot, and that this use case is frequent enough to contemplate eventually making it the only in-line function syntax. -1 from me. I think that lambda / inline functions should be discouraged as it moves python away from, there should be one-- and preferably only one --obvious way to do it. IMHO Guido was right in his original impulse to kill this second class way of making functions... I would write the above as def compute_key(n): Compute the sort key so that x, y and z are true return n % 3 sorted(range(9), key=compute_key) Which I think is clearer and more obvious. It gives you the opportunity for a docstring also. Yes it is a bit more typing, but who wants to play code golf all day? -- Nick Craig-Wood n...@craig-wood.com -- http://www.craig-wood.com/nick -- http://mail.python.org/mailman/listinfo/python-list
Re: Special keyword argument lambda syntax
On Mar 14, 5:30 pm, Nick Craig-Wood n...@craig-wood.com wrote: BeniCherniavskybeni.cherniav...@gmail.com wrote: This proposal outrageously suggests a special syntax for in-line functions passed as keyword arguments:: sorted(range(9), key(n)=n%3) [0, 3, 6, 1, 4, 7, 2, 5, 8] The claim is that such specialization hits a syntax sweet spot, and that this use case is frequent enough to contemplate eventually making it the only in-line function syntax. -1 from me. I think thatlambda/ inline functions should be discouraged as it moves python away from, there should be one-- and preferably only one --obvious way to do it. IMHO Guido was right in his original impulse to kill this second class way of making functions... On a second thought, considering the LL(1) problem (which indicates a real problem for humans parsing it) and the f(x)== confusion, I agree. Given that ``lambda`` usage is negligible compared to ``def`` (1.5% in python3.0 stdlib, ~3% counting most Python files in ubuntu repository), it should have been killed altogether per YAGNI and the one way principle. [Or is it just my if you don't do it my way, don't do it at all emotion talking? Don't know. But I did the statistics only after formulating the proposal, and I think now that 3% is definitely YAGNI.] -- http://mail.python.org/mailman/listinfo/python-list
Re: Special keyword argument lambda syntax
On Fri, 13 Mar 2009 16:39:16 -, Scott David Daniels scott.dani...@acm.org wrote: The original proposal was initially appealing to me until I saw this comment. That means a relatively invisible typo would turn into good syntax. Possibley this is exactly what Rhodri James is talking about, but just to be explicit, one of these is probably a mistake: somefun(something, key(x)==5) somefun(something, key(x)=5) Right now a syntax error makes you look there, after your extension, only test cases will show these problems. Oo, no, I'd missed that! Good catch. -- Rhodri James *-* Wildebeeste Herder to the Masses -- http://mail.python.org/mailman/listinfo/python-list
Re: Special keyword argument lambda syntax
On Fri, 13 Mar 2009 15:33:26 -, MRAB goo...@mrabarnett.plus.com wrote: Rhodri James wrote: On Fri, 13 Mar 2009 14:49:17 -, Beni Cherniavsky beni.cherniav...@gmail.com wrote: Specification = Allow keyword arguments in function call to take this form: NAME ( ARGUMENTS ) = EXPRESSION which is equivallent to the following: NAME = lambda ARGUMENTS: EXPRESSION except that NAME is also assigned as the function's `__name__`. My first instinct on seeing the example was that key(n) was a function *call*, not a function definition, and to remember the thread a month or two ago about assigning to the result of a function call. I'm inclined to think this would add confusion rather than remove it. Guido wants to keep the syntax LL(1), so you're not the only one who has a problem with it! :-) I think that: def NAME ( ARGUMENTS ): EXPRESSION is still LL(1). Yes, but at this point we're arguing about how to spell lambda, and Python's already got one perfectly good way of spelling it. -- Rhodri James *-* Wildebeeste Herder to the Masses -- http://mail.python.org/mailman/listinfo/python-list
Special keyword argument lambda syntax
This proposal (a) ignores Guido's clear-cut decision that lambda is good as it is, (b) is weird in proposing a special-case syntax, (c) is several Python versions too late for a graceful transition by 3.0. But I don't won't to just throw the idea away, so I'm posting here. If there is serious positive feedback proving I'm not crazy, I'll make a PEP. Abstract This proposal outrageously suggests a special syntax for in-line functions passed as keyword arguments:: sorted(range(9), key(n)=n%3) [0, 3, 6, 1, 4, 7, 2, 5, 8] The claim is that such specialization hits a syntax sweet spot, and that this use case is frequent enough to contemplate eventually making it the only in-line function syntax. Specification = Allow keyword arguments in function call to take this form: NAME ( ARGUMENTS ) = EXPRESSION which is equivallent to the following: NAME = lambda ARGUMENTS: EXPRESSION except that NAME is also assigned as the function's `__name__`. Motivation == ``lambda`` is widely considered arbitrary and ugly, as proven by the numerous proposals for alternative syntax. It's also widely considered good enough, as proven by said proposals being consistently shot down ;-). The proposed syntax solves the following drawbacks of lambda: - It's not obvious from the look of ``lambda n: n % 3`` that it defines a function. ``key(n) = n % 3`` is arguably so clear intuitively, that it won't a non-familiar reader won't have to stop and look it up. (The ability to look lambda up is cited as one of the main reasons to keep it.) - A long meaningless (for non-lisp-geeks) keyword in the middle of code. - The use of ``:`` to delimit the lambda body is misleading - people expect ``:`` to be followed by a statement, not an expression. - Lambda functions are anonymous, which makes their origin harder to recognize when debugging. The proposed syntax allows the keyword argument to also serve as the function name, giving a (somewhat) meaningful name without any naming effort from the user. However nice this syntax, why should we consider something targeted at the special case of keyword arguments? 1. It is an important use case. Consider lambda usage in the 3.0 stdlib: * 22 times (ab)used as stand-alone shorthand to ``def``. * 18 times passed to `map()` / `filter()` - most are old code predating list comprehensions (given away by ``x=x`` hack predating nested scopes). * 4 times passed to `property()` - now better written as `...@property`` def. * 25 times used as legitimate positional argument (not one of the above). * 31 times used as a keyword argument. * 6 times used in other constructs. So keyword cover about half of the good uses of lambda, and many uses as positional arguments can be converted to keyword arguments, sometimes improving readability (cf. 3.0's conversion of `key` and `reverse` arguments to keyword-only). 2. We don't have to cover *all* use cases - remember that one can always fall back on ``def`` (which BTW is used ~10250 times in stdlib, making all uses of lambda total 1% of uses of ``def``, making one wonder if we need in-line function syntax at all). So one can imagine this syntax one day replacing most uses of ``lambda``, at which point ``lambda`` can be killed altogether. Optional extension = Given this syntax for keyword arguments, users might expect it to also word as a standalone statement: NAME ( ARGUMENTS ) = EXPRESSION which is equivallent to the following: def NAME ( ARGUMENTS): return EXPRESSION Should we allow it? People abuse ``lambda`` in this way already (see above stdlib statistics), this is just a cleaner version. But this syntax has no place for a docstring, so allowing it will encourage people to write functions without docstings. Opinions anybody? -- http://mail.python.org/mailman/listinfo/python-list
Re: Special keyword argument lambda syntax
On Fri, 13 Mar 2009 14:49:17 -, Beni Cherniavsky beni.cherniav...@gmail.com wrote: Specification = Allow keyword arguments in function call to take this form: NAME ( ARGUMENTS ) = EXPRESSION which is equivallent to the following: NAME = lambda ARGUMENTS: EXPRESSION except that NAME is also assigned as the function's `__name__`. My first instinct on seeing the example was that key(n) was a function *call*, not a function definition, and to remember the thread a month or two ago about assigning to the result of a function call. I'm inclined to think this would add confusion rather than remove it. -- Rhodri James *-* Wildebeeste Herder to the Masses -- http://mail.python.org/mailman/listinfo/python-list
Re: Special keyword argument lambda syntax
Rhodri James wrote: On Fri, 13 Mar 2009 14:49:17 -, Beni Cherniavsky beni.cherniav...@gmail.com wrote: Specification = Allow keyword arguments in function call to take this form: NAME ( ARGUMENTS ) = EXPRESSION which is equivallent to the following: NAME = lambda ARGUMENTS: EXPRESSION except that NAME is also assigned as the function's `__name__`. My first instinct on seeing the example was that key(n) was a function *call*, not a function definition, and to remember the thread a month or two ago about assigning to the result of a function call. I'm inclined to think this would add confusion rather than remove it. Guido wants to keep the syntax LL(1), so you're not the only one who has a problem with it! :-) I think that: def NAME ( ARGUMENTS ): EXPRESSION is still LL(1). For example: sorted(range(9), def key(n): n % 3) [0, 3, 6, 1, 4, 7, 2, 5, 8] -- http://mail.python.org/mailman/listinfo/python-list
Re: Special keyword argument lambda syntax
Rhodri James wrote: On Fri, 13 Mar 2009 14:49:17 -, Beni Cherniavsky beni.cherniav...@gmail.com wrote: ...Allow keyword arguments in function call to take this form: NAME ( ARGUMENTS ) = EXPRESSION which is equivallent to the following: NAME = lambda ARGUMENTS: EXPRESSION except that NAME is also assigned as the function's `__name__`. My first instinct on seeing the example was that key(n) was a function *call*, not a function definition, and to remember the thread a month or two ago about assigning to the result of a function call. I'm inclined to think this would add confusion rather than remove it. The original proposal was initially appealing to me until I saw this comment. That means a relatively invisible typo would turn into good syntax. Possibley this is exactly what Rhodri James is talking about, but just to be explicit, one of these is probably a mistake: somefun(something, key(x)==5) somefun(something, key(x)=5) Right now a syntax error makes you look there, after your extension, only test cases will show these problems. --Scott David Daniels scott.dani...@acm.org -- http://mail.python.org/mailman/listinfo/python-list
Re: Special keyword argument lambda syntax
MRAB goo...@mrabarnett.plus.com writes: sorted(range(9), def key(n): n % 3) [0, 3, 6, 1, 4, 7, 2, 5, 8] Given the recent pattern of syntactic constructs for expressions using expr keyword expr (ternary if, listcomps, genexps), and avoiding the use of colon in expressions, maybe it should be: sorted(range(9), key=n % 3 def key(n)) this is analogous to sorted(range(9), foo=n % 3 if bla(n)) It also shares the property that it reuses an existing keyword and avoids the word lambda, originally (I presume) an homage to Church, now considered obscure-sounding by many. -- http://mail.python.org/mailman/listinfo/python-list
Re: Special keyword argument lambda syntax
Hrvoje Niksic wrote: MRAB goo...@mrabarnett.plus.com writes: sorted(range(9), def key(n): n % 3) [0, 3, 6, 1, 4, 7, 2, 5, 8] Given the recent pattern of syntactic constructs for expressions using expr keyword expr (ternary if, listcomps, genexps), and avoiding the use of colon in expressions, maybe it should be: sorted(range(9), key=n % 3 def key(n)) this is analogous to sorted(range(9), foo=n % 3 if bla(n)) It also shares the property that it reuses an existing keyword and avoids the word lambda, originally (I presume) an homage to Church, now considered obscure-sounding by many. If you want to avoid the colon then: sorted(range(9), def key(n)=n % 3) [0, 3, 6, 1, 4, 7, 2, 5, 8] which would be syntactic sugar for: sorted(range(9), key=lambda n: n % 3) -- http://mail.python.org/mailman/listinfo/python-list
Re: Special keyword argument lambda syntax
MRAB: sorted(range(9), def key(n): n % 3) I am fine with the current lambda syntax, but another possibility: sorted(range(9), n = n % 3) Bye, bearophile -- http://mail.python.org/mailman/listinfo/python-list
