Re: Avoiding local variable declarations?
greg [EMAIL PROTECTED] wrote: I've only ever seen identity element in English mathematics. Neutral element sounds like something my car's gearbox might have... I've encountered both. I think `neutral element' is more common when dealing with the possibility that it might not be unique (in the way that identity elements are in groups, rings and fields), but that might just be my misconception. -- [mdw] -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
greg [EMAIL PROTECTED] writes: Arnaud Delobelle wrote: Neutral element is correct. But maybe its use is limited to mathematicians in the english-speaking word. I've only ever seen identity element in English mathematics. Neutral element sounds like something my car's gearbox might have... I was an academic mathematician for several years (although not a very good one) and I can assure you that 'neutral element' is correct and understood. 'Unit element' is another common synonym. Unfortunately I can't find a reference in one of the few books in English that I have at home. Lang's Algebra does not seem to use the term and it's the only undergraduate book I've got. Wikipedia and other internet sources cite 'neutral element' as a synonym to 'identity element'. -- Arnaud -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
Marc 'BlackJack' Rintsch [EMAIL PROTECTED] writes: On Tue, 18 Nov 2008 00:18:51 +, Steven D'Aprano wrote: On Mon, 17 Nov 2008 12:32:35 +, Marc 'BlackJack' Rintsch wrote: Not such illogical crap like ``a = a + 1`` which must be obviously false unless 1 is defined as the neutral element for the definition of ``+`` here. I don't quite know what you mean by neutral element. I think you mean the identity element […] I knew I should have looked it up instead of translating it from my mother tongue -- yes I ment identity element. Sorry for the confusion. Neutral element is correct. But maybe its use is limited to mathematicians in the english-speaking word. -- Arnaud -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
En Tue, 18 Nov 2008 16:27:46 -0200, Arnaud Delobelle [EMAIL PROTECTED] escribió: Marc 'BlackJack' Rintsch [EMAIL PROTECTED] writes: On Tue, 18 Nov 2008 00:18:51 +, Steven D'Aprano wrote: On Mon, 17 Nov 2008 12:32:35 +, Marc 'BlackJack' Rintsch wrote: Not such illogical crap like ``a = a + 1`` which must be obviously false unless 1 is defined as the neutral element for the definition of ``+`` here. I don't quite know what you mean by neutral element. I think you mean the identity element […] I knew I should have looked it up instead of translating it from my mother tongue -- yes I ment identity element. Sorry for the confusion. Neutral element is correct. But maybe its use is limited to mathematicians in the english-speaking word. In Spanish I've seen elemento neutro and elemento identidad used interchangeably. -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
Arnaud Delobelle wrote: Neutral element is correct. But maybe its use is limited to mathematicians in the english-speaking word. I've only ever seen identity element in English mathematics. Neutral element sounds like something my car's gearbox might have... -- Greg -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
On Thu, 13 Nov 2008 12:49:02 -0800 (PST), dpapathanasiou [EMAIL PROTECTED] wrote: ... but what's wrong with you original code? I come from a functional programming school of thought, where you avoid local variable declarations if at all possible. I'm not sure that's universal. Using Standard ML at Uni, it was often useful to use let name = expr in expr (or whatever the syntax was) to simplify an expression. Directly borrowed from mathematics, I assume. 'name' is not a variable, of course; there are no variables in functional programming. Can't remember what it's called -- named expression, maybe? I think I use local names in Python about as much as I did in SML. /Jorgen -- // Jorgen Grahn grahn@Ph'nglui mglw'nafh Cthulhu \X/ snipabacken.se R'lyeh wgah'nagl fhtagn! -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
On Mon, 17 Nov 2008 10:10:16 +, Jorgen Grahn wrote: On Thu, 13 Nov 2008 12:49:02 -0800 (PST), dpapathanasiou [EMAIL PROTECTED] wrote: ... but what's wrong with you original code? I come from a functional programming school of thought, where you avoid local variable declarations if at all possible. I'm not sure that's universal. Using Standard ML at Uni, it was often useful to use let name = expr in expr (or whatever the syntax was) to simplify an expression. Directly borrowed from mathematics, I assume. That's (also?) Haskell syntax and I agree that it is useful to write readable code. 'name' is not a variable, of course; there are no variables in functional programming. Can't remember what it's called -- named expression, maybe? I think it's called variable and works like variables work in mathematics, i.e. you can assign only once. Not such illogical crap like ``a = a + 1`` which must be obviously false unless 1 is defined as the neutral element for the definition of ``+`` here. :-) Ciao, Marc 'BlackJack' Rintsch -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
On Mon, 17 Nov 2008 12:32:35 +, Marc 'BlackJack' Rintsch wrote: Not such illogical crap like ``a = a + 1`` which must be obviously false unless 1 is defined as the neutral element for the definition of ``+`` here. I don't quite know what you mean by neutral element. I think you mean the identity element under addition, which is zero, but that doesn't work: 0 = 0 + 1 Obviously not. I think the only workable answer might be a = infinity, but that has two problems: (1) infinity isn't a valid integer or real number (although there is a valid float representing infinity on many platforms); and (2) which infinity? Aleph 0, aleph 1, c, ... There's an infinite number of them. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
En Mon, 17 Nov 2008 22:18:51 -0200, Steven D'Aprano [EMAIL PROTECTED] escribió: On Mon, 17 Nov 2008 12:32:35 +, Marc 'BlackJack' Rintsch wrote: Not such illogical crap like ``a = a + 1`` which must be obviously false unless 1 is defined as the neutral element for the definition of ``+`` here. I don't quite know what you mean by neutral element. I think you mean the identity element under addition, which is zero, but that doesn't work: 0 = 0 + 1 Obviously not. Perhaps you didn't read carefully the above post? He said unless *1* is defined as the neutral element for ``+`` Calling 1 the identity of the + operation, or calling + an operation having 1 as its identity element is, errr, uncommon at least, but perfectly valid... -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
On Nov 17, 5:12 pm, Gabriel Genellina [EMAIL PROTECTED] wrote: En Mon, 17 Nov 2008 22:18:51 -0200, Steven D'Aprano [EMAIL PROTECTED] escribió: On Mon, 17 Nov 2008 12:32:35 +, Marc 'BlackJack' Rintsch wrote: Not such illogical crap like ``a = a + 1`` which must be obviously false unless 1 is defined as the neutral element for the definition of ``+`` here. I don't quite know what you mean by neutral element. I think you mean the identity element under addition, which is zero, but that doesn't work: 0 = 0 + 1 Obviously not. Perhaps you didn't read carefully the above post? He said unless *1* is defined as the neutral element for ``+`` Calling 1 the identity of the + operation, or calling + an operation having 1 as its identity element is, errr, uncommon at least, but perfectly valid... -- Gabriel Genellina def __add__(self, other): return self + other - 1 Don't tell me this is not Pythonic! -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
On Mon, 17 Nov 2008 23:12:25 -0200, Gabriel Genellina wrote: Perhaps you didn't read carefully the above post? Er, yes, you got me on that. :( -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
On Tue, 18 Nov 2008 00:18:51 +, Steven D'Aprano wrote: On Mon, 17 Nov 2008 12:32:35 +, Marc 'BlackJack' Rintsch wrote: Not such illogical crap like ``a = a + 1`` which must be obviously false unless 1 is defined as the neutral element for the definition of ``+`` here. I don't quite know what you mean by neutral element. I think you mean the identity element […] I knew I should have looked it up instead of translating it from my mother tongue -- yes I ment identity element. Sorry for the confusion. Ciao, Marc 'BlackJack' Rintch -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
Paul McGuire: Really? Looking at randrange, it sure seems to do a lot of work in pursuit of handling all possible cases for specifying range boundaries, step values, etc. Well, randrange is the simpler thing to read and understand here, and maybe the one less likely to get wrong too. But I understand your concerns. The solution is to write a C function in the random module that implements the randrange in an efficient way. Bye, bearophile -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
Chris Mellon [EMAIL PROTECTED] wrote: Any time you port between languages, it's rarely a good idea to just convert code verbatim. For example: import random, string def random_char(): return random.choice(string.ascii_letters + string.digits) Note that this code doesn't preserve the output distribution of the original, for which once expects half the characters to be numeric. I don't know if that's relevant; in fact I suspect that the original was buggy. -- [mdw] -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
On Nov 14, 12:08 pm, Mark Wooding [EMAIL PROTECTED] wrote: Chris Mellon [EMAIL PROTECTED] wrote: Any time you port between languages, it's rarely a good idea to just convert code verbatim. For example: import random, string def random_char(): return random.choice(string.ascii_letters + string.digits) Note that this code doesn't preserve the output distribution of the original, for which once expects half the characters to be numeric. I don't know if that's relevant; in fact I suspect that the original was buggy. -- [mdw] I couldn't have said it better myself. Well, if not better, at least earlier... (http://groups.google.com/group/comp.lang.python/msg/580779bf57e4d3a0? hl=en) -- Paul -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
On Thu, Nov 13, 2008 at 2:22 PM, dpapathanasiou [EMAIL PROTECTED] wrote: I have some old Common Lisp functions I'd like to rewrite in Python (I'm still new to Python), and one thing I miss is not having to declare local variables. For example, I have this Lisp function: (defun random-char () Generate a random char from one of [0-9][a-z][A-Z] (if ( 50 (random 100)) (code-char (+ (random 10) 48)) ; ascii 48 = 0 (code-char (+ (random 26) (if ( 50 (random 100)) 65 97) ; ascii 65 = A, 97 = a My Python version looks like this: def random_char (): '''Generate a random char from one of [0-9][a-z][A-Z]''' if random.randrange(0, 100) 50: return chr( random.randrange(0, 10) + 48 ) # ascii 48 = 0 else: offset = 65 # ascii 65 = A if random.randrange(0, 100) 50: offset = 97 # ascii 97 = a return chr( random.randrange(0, 26) + offset ) Logically, it's equivalent of the Lisp version. But is there any way to avoid using the local variable (offset) in the Python version? Any time you port between languages, it's rarely a good idea to just convert code verbatim. For example: import random, string def random_char(): return random.choice(string.ascii_letters + string.digits) -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
dpapathanasiou wrote: I have some old Common Lisp functions I'd like to rewrite in Python (I'm still new to Python), and one thing I miss is not having to declare local variables. For example, I have this Lisp function: (defun random-char () Generate a random char from one of [0-9][a-z][A-Z] (if ( 50 (random 100)) (code-char (+ (random 10) 48)) ; ascii 48 = 0 (code-char (+ (random 26) (if ( 50 (random 100)) 65 97) ; ascii 65 = A, 97 = a My Python version looks like this: def random_char (): '''Generate a random char from one of [0-9][a-z][A-Z]''' if random.randrange(0, 100) 50: return chr( random.randrange(0, 10) + 48 ) # ascii 48 = 0 else: offset = 65 # ascii 65 = A if random.randrange(0, 100) 50: offset = 97 # ascii 97 = a return chr( random.randrange(0, 26) + offset ) Logically, it's equivalent of the Lisp version. But is there any way to avoid using the local variable (offset) in the Python version? Yes, you can avoid using offset, but *why*. This certainly won't make your code cleaner or more easily read/understood/maintainable. return chr( random.randrange(0, 26) + (97 if random.randrange(0, 100) 50 else 65) or if random.randrange(0, 100) 50: return chr( random.randrange(0, 26) + 97) else: return chr( random.randrange(0, 26) + 65) or return chr( random.randrange(0, 26) + [26,97][random.randrange(0, 100) 50] or ... probably other ways can be found ... but what's wrong with you original code? Gary Herron -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
return chr( random.randrange(0, 26) + (97 if random.randrange(0, 100) 50 else 65) or return chr( random.randrange(0, 26) + [26,97][random.randrange(0, 100) 50] Ah, thanks, these are the syntax examples I was looking for. but what's wrong with you original code? I come from a functional programming school of thought, where you avoid local variable declarations if at all possible. -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
Any time you port between languages, it's rarely a good idea to just convert code verbatim. For example: import random, string def random_char(): return random.choice(string.ascii_letters + string.digits) Good point, and thanks for the idiomatic Python example (I like the conciseness); I'm still wrapping my mind around how Python statements should be constructed. -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
Gary Herron [EMAIL PROTECTED] wrote in message news:[EMAIL PROTECTED] return chr( random.randrange(0, 26) + [26,97][random.randrange(0, 100) 50] return chr(random.randrange(0, 26) + (97 if random.randrange(0,100) 50 else 26)) -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
In article [EMAIL PROTECTED], dpapathanasiou [EMAIL PROTECTED] wrote: I come from a functional programming school of thought, where you avoid local variable declarations if at all possible. Python is *so* not a functional programming language. There are a number of functional programming features available, but trying to push your Python programs into primarily a functional style will result in significantly poorer Python programs. Find another language if functional programming is critical to your style. -- Aahz ([EMAIL PROTECTED]) * http://www.pythoncraft.com/ It is easier to optimize correct code than to correct optimized code. --Bill Harlan -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
On Nov 13, 2:32 pm, Chris Mellon [EMAIL PROTECTED] wrote: On Thu, Nov 13, 2008 at 2:22 PM, dpapathanasiou [EMAIL PROTECTED] wrote: I have some old Common Lisp functions I'd like to rewrite in Python (I'm still new to Python), and one thing I miss is not having to declare local variables. For example, I have this Lisp function: (defun random-char () Generate a random char from one of [0-9][a-z][A-Z] (if ( 50 (random 100)) (code-char (+ (random 10) 48)) ; ascii 48 = 0 (code-char (+ (random 26) (if ( 50 (random 100)) 65 97) ; ascii 65 = A, 97 = a My Python version looks like this: def random_char (): '''Generate a random char from one of [0-9][a-z][A-Z]''' if random.randrange(0, 100) 50: return chr( random.randrange(0, 10) + 48 ) # ascii 48 = 0 else: offset = 65 # ascii 65 = A if random.randrange(0, 100) 50: offset = 97 # ascii 97 = a return chr( random.randrange(0, 26) + offset ) Logically, it's equivalent of the Lisp version. But is there any way to avoid using the local variable (offset) in the Python version? Any time you port between languages, it's rarely a good idea to just convert code verbatim. For example: import random, string def random_char(): return random.choice(string.ascii_letters + string.digits)- Hide quoted text - - Show quoted text - Not quite. The original Lisp function first flips a coin to see if a digit or alpha should be returned. If alpha, then flips a coin again to see if upper or lower case should be returned. The alpha branch could be collapsed into just returning a random selection from [A-Za- z], but if you combine the alpha and numeric branches, you have less than a 1/3 chance of getting a digit, vs. the 50-50 chance of the original Lisp code. Try this: import random import string coinflip = lambda : int(random.random()*2) if coinflip(): return random.choice(string.digits) else: return random.choice(string.ascii_letters) or just: return random.choice( (string.digits, string.ascii_letters)[coinflip ()] ) -- Paul -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
Paul McGuire: coinflip = lambda : int(random.random()*2) I warmly suggest you to use this instead: randrange(2) Bye, bearophile -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
On Nov 13, 6:47 pm, [EMAIL PROTECTED] wrote: Paul McGuire: coinflip = lambda : int(random.random()*2) I warmly suggest you to use this instead: randrange(2) Bye, bearophile Really? Looking at randrange, it sure seems to do a lot of work in pursuit of handling all possible cases for specifying range boundaries, step values, etc. In fact, I think flipping a coin is a common enough task that it might even merit an addition to the random module API. It certainly would allow us to get rid of all of these variations on the theme, such as if randrange(100) 50, or random.choice([True,False]). For that matter, my own obscure int (random.random() * 2) is better implemented using a direct comparison to random.random(), no need for multiplication, or int calls or anything else. Having an explicit method would also help prevent minor erroneous bugs like if random.random() 0.5, given that the range of random.random() is (0.0, 1.0] (that is, the lower half would be 0 inclusive to 0.5 exclusive, and the upper half 0.5 inclusive to 1.0 exclusive). If I would change anything, I think I prefer the name coin_toss over coinflip. So: coin_toss = lambda : random.random() = 0.5 -- Paul -- http://mail.python.org/mailman/listinfo/python-list
Re: Avoiding local variable declarations?
dpapathanasiou [EMAIL PROTECTED] writes: but what's wrong with you original code? I come from a functional programming school of thought, where you avoid local variable declarations if at all possible. Holding on to this principle won't help you write nice Python code :) Although you will acquire lots of clever-looking tricks. -- Arnaud -- http://mail.python.org/mailman/listinfo/python-list
