On Sat, 24 Dec 2011 19:41:55 +0100, Thomas Rachel wrote:
>> The only times you need the brackets around a tuple is to control the
>> precedence of operations, or for an empty tuple.
>
> IBTD:
>
> a=((a, b) for a, b, c in some_iter)
> b=[(1, c) for ]
>
> Without the round brackets, it is a synta
On 12/24/2011 07:25 PM, Steven D'Aprano wrote:
I'd use a function attribute.
def func(x, y=None):
if y is None:
y = func.default_y
...
func.default_y = []
That's awkward only if you believe function attributes are awkward.
I do. All you've done is move the default from *before* the
On Dec 25, 5:32 am, Devin Jeanpierre wrote:
> alex23 wrote:
> > Because I believe that the source of confusion has far more to do with
> > mutable/immutable objects than with early/late binding. Masking or
> > 'correcting' an aspect of Python's behaviour because novices make the
> > wrong assumpti
> Because I believe that the source of confusion has far more to do with
> mutable/immutable objects than with early/late binding. Masking or
> 'correcting' an aspect of Python's behaviour because novices make the
> wrong assumption about it just pushes the problem elsewhere and
> potentially makes
On Dec 25, 9:25 am, Devin Jeanpierre wrote:
> > If Python was ever 'fixed' to prevent this issue, I'm pretty sure we'd
> > see an increase in the number of questions like the OP's.
>
> What makes you so sure? Both models do make sense and are equally
> valid, it's just that only one of them is tru
> If Python was ever 'fixed' to prevent this issue, I'm pretty sure we'd
> see an increase in the number of questions like the OP's.
What makes you so sure? Both models do make sense and are equally
valid, it's just that only one of them is true. Is it just because
people already used to Python wo
Am 22.12.2011 00:20 schrieb Dennis Lee Bieber:
The key one is that lists ([] defines a list, not an array) are
"mutable". Your "7" is not mutable.
Strictly spoken, that's only a "side show" where the effect is visible.
The real key concept is that [] creates *one* object which is then
Am 22.12.2011 00:48 schrieb Steven D'Aprano:
On Wed, 21 Dec 2011 18:20:16 -0500, Dennis Lee Bieber wrote:
For the amount of typing, it's easier to just do a straight line
tuple unpack
a,b,c = ([],[],[])
Note that tuples are created by the comma, not the round brackets (or
parenthese
Am 21.12.2011 23:25 schrieb Eric:
Is it true that if I want to create an array or arbitrary size such
as:
for a in range(n):
x.append()
I must do this instead?
x=[]
for a in range(n):
x.append()
Of course - your x must exist before using it.
> Now to my actual quest
On Dec 24, 6:25 pm, Steven D'Aprano wrote:
> > It's
> > much harder to figure out what's going wrong with an early-bound
> > mutable.
>
> Only for those who don't understand, or aren't thinking about, Python's
> object model. The behaviour of early-bound mutables is obvious and clear
> once you th
On Dec 24, 2:15 am, Roy Smith wrote:
> I know this is not quite the same thing, but it's interesting to look at
> what django (and mongoengine) do in their model definitions, prompted by
> your time.time() example. You can do declare a model field something
> like:
>
> class Foo(models.Model):
>
On Dec 24, 2:27 am, Mel Wilson wrote:
> In a tool that's meant for other people to use to accomplish work of their
> own, breaking workflow is a cardinal sin.
>
> In a research language that's meant always to be up-to-date with the concept
> of the week, not so much.
What on earth gave you the im
On 12/22/2011 10:20 AM, Dennis Lee Bieber wrote:
which is to define the names "a", "b", and "c", and connects the three
names to the single object (integer 7 or new empty list).
note that this "connects" and "disconnecting" business is more commonly
referred to in python parlance as "binding"
On Fri, 23 Dec 2011 19:24:44 -0500, Devin Jeanpierre wrote:
>> To fake early binding when the language provides late binding, you
>> still use a sentinel value, but the initialization code creating the
>> default value is outside the body of the function, usually in a global
>> variable:
>>
>>
On Fri, 23 Dec 2011 17:03:11 +, Neil Cerutti wrote:
>> The disadvantage of late binding is that since the expression is live,
>> it needs to be calculated each time, even if it turns out to be the
>> same result. But there's no guarantee that it will return the same
>> result each time:
>
> T
On Sat, 24 Dec 2011 09:50:04 +1100, Chris Angelico wrote:
> On Sat, Dec 24, 2011 at 9:32 AM, Steven D'Aprano
> wrote:
>> Yes. But having to manage it *by hand* is still unclean:
>
> Well, my point was that Python's current behaviour _is_ that.
Minus the managing it by hand part.
>> * you stil
> To fake early binding when the language provides late binding, you still
> use a sentinel value, but the initialization code creating the default
> value is outside the body of the function, usually in a global variable:
>
>_DEFAULT_Y = [] # Private constant, don't touch.
>
>def func(x,
On Sat, Dec 24, 2011 at 9:32 AM, Steven D'Aprano
wrote:
> Yes. But having to manage it *by hand* is still unclean:
Well, my point was that Python's current behaviour _is_ that.
> * you still have to assign the default value to the function assignment
> outside the function, which is inelegant;
On Sat, 24 Dec 2011 02:55:41 +1100, Chris Angelico wrote:
> On Sat, Dec 24, 2011 at 2:49 AM, Steven D'Aprano
> wrote:
>> To fake early binding when the language provides late binding, you
>> still use a sentinel value, but the initialization code creating the
>> default value is outside the body
On 12/23/2011 03:31 AM, rusi wrote:
> In Fortran, if the comma in the loop
> DO 10 I = 1,10
> is misspelt as '.' it becomes the assignment
> DO10I = 1.0
>
> Do you consider it a bug or a feature?
> Does Fortran consider it a bug or feature?
Non sequitor. Nothing at all to do with the issue at ha
On 2011-12-23, Steven D'Aprano wrote:
> On Fri, 23 Dec 2011 13:13:38 +, Neil Cerutti wrote:
>> On 2011-12-23, Neil Cerutti wrote:
>>> Is the misfeature that Python doesn't evaluate the default
>>> argument expression every time you call the function? What
>>> would be the harm if it did?
>>
Steven D'Aprano wrote:
> On Fri, 23 Dec 2011 13:13:38 +, Neil Cerutti wrote:
>> On 2011-12-23, Neil Cerutti wrote:
>> ...you know, assuming it wouldn't break existing code. ;)
>
> It will. Python's default argument strategy has been in use for 20 years.
> Some code will rely on it. I know min
In article <4ef4a30d$0$29973$c3e8da3$54964...@news.astraweb.com>,
Steven D'Aprano wrote:
> The disadvantage of late binding is that since the expression is live, it
> needs to be calculated each time, even if it turns out to be the same
> result. But there's no guarantee that it will return th
On Dec 23, 8:33 pm, Steven D'Aprano wrote:
> On Fri, 23 Dec 2011 06:57:02 -0800, rusi wrote:
> > On Dec 23, 6:53 pm, Robert Kern wrote:
> >> On 12/23/11 1:23 PM, rusi wrote:
> [...]
> >> > Of course it should be fixed. The repeated recurrence of it as a
> >> > standard gotcha as well as the pyth
On Sat, Dec 24, 2011 at 2:49 AM, Steven D'Aprano
wrote:
> To fake early binding when the language provides late binding, you still
> use a sentinel value, but the initialization code creating the default
> value is outside the body of the function, usually in a global variable:
>
> _DEFAULT_Y =
On Fri, 23 Dec 2011 13:13:38 +, Neil Cerutti wrote:
> On 2011-12-23, Neil Cerutti wrote:
>> Is the misfeature that Python doesn't evaluate the default argument
>> expression every time you call the function? What would be the harm if
>> it did?
>
> ...you know, assuming it wouldn't break exi
On Fri, 23 Dec 2011 06:57:02 -0800, rusi wrote:
> On Dec 23, 6:53 pm, Robert Kern wrote:
>> On 12/23/11 1:23 PM, rusi wrote:
[...]
>> > Of course it should be fixed. The repeated recurrence of it as a
>> > standard gotcha as well as the python ideas list testifies to that.
>>
>> So you were lyin
On Dec 23, 6:53 pm, Robert Kern wrote:
> On 12/23/11 1:23 PM, rusi wrote:
>
>
>
>
>
>
>
>
>
> > On Dec 23, 6:10 pm, Robert Kern wrote:
> >> On 12/23/11 10:22 AM, rusi wrote:
> >>> On Dec 23, 2:39 pm, Steven D'Aprano >>> +comp.lang.pyt...@pearwood.info> wrote:
> Some people might argue tha
On 12/23/11 1:23 PM, rusi wrote:
On Dec 23, 6:10 pm, Robert Kern wrote:
On 12/23/11 10:22 AM, rusi wrote:
On Dec 23, 2:39 pm, Steven D'Apranowrote:
Some people might argue that it is a mistake, a minor feature which
allegedly causes more difficulties than benefits. I do not hold with th
On Dec 23, 6:10 pm, Robert Kern wrote:
> On 12/23/11 10:22 AM, rusi wrote:
>
>
>
>
>
>
>
>
>
> > On Dec 23, 2:39 pm, Steven D'Aprano > +comp.lang.pyt...@pearwood.info> wrote:
> >> On Fri, 23 Dec 2011 00:38:07 -0800, rusi wrote:
> >>> Likewise function arguments that default to mutable entities is
On 2011-12-23, Chris Angelico wrote:
> On Fri, Dec 23, 2011 at 7:49 PM, Ethan Furman wrote:
>> That is the most ridiculous thing I have heard in a while.
>> ?Mutable default arguments are *not* a bug in Python.
>>
>> Reminds me of a bug report a couple years back claiming
>> multiple inheritence
On 2011-12-23, Neil Cerutti wrote:
> Is the misfeature that Python doesn't evaluate the default
> argument expression every time you call the function? What
> would be the harm if it did?
...you know, assuming it wouldn't break existing code. ;)
--
Neil Cerutti
--
http://mail.python.org/mailma
On 12/23/11 10:22 AM, rusi wrote:
On Dec 23, 2:39 pm, Steven D'Aprano wrote:
On Fri, 23 Dec 2011 00:38:07 -0800, rusi wrote:
Likewise function arguments that default to mutable entities is a known
gotcha of python which is best treated as a bug in python.
Nonsense. It is a feature, not a bug
On Dec 23, 2:39 pm, Steven D'Aprano wrote:
> On Fri, 23 Dec 2011 00:38:07 -0800, rusi wrote:
> > Likewise function arguments that default to mutable entities is a known
> > gotcha of python which is best treated as a bug in python.
>
> Nonsense. It is a feature, not a bug.
Tsk Tsk How can python
On Dec 23, 2:59 pm, Chris Angelico wrote:
> On Fri, Dec 23, 2011 at 7:49 PM, Ethan Furman wrote:
> > That is the most ridiculous thing I have heard in a while. Mutable default
> > arguments are *not* a bug in Python.
>
> > Reminds me of a bug report a couple years back claiming multiple inherite
On Fri, Dec 23, 2011 at 7:49 PM, Ethan Furman wrote:
> That is the most ridiculous thing I have heard in a while. Mutable default
> arguments are *not* a bug in Python.
>
> Reminds me of a bug report a couple years back claiming multiple inheritence
> was a bug and asking it to be removed.
Both
rusi wrote:
On Dec 23, 7:10 am, alex23 wrote:
On Dec 22, 6:51 pm, Rolf Camps wrote:
I'm afraid it's dangerous to encourage the use of '[]' as assignment to
a parameter in a function definition. If you use the function several
times 'default' always points to the same list.
>>
I appreciate
On Fri, 23 Dec 2011 00:38:07 -0800, rusi wrote:
> Likewise function arguments that default to mutable entities is a known
> gotcha of python which is best treated as a bug in python.
Nonsense. It is a feature, not a bug.
Some people might argue that it is a mistake, a minor feature which
allege
Ian Kelly wrote:
On Thu, Dec 22, 2011 at 7:10 PM, alex23 wrote:
On Dec 22, 6:51 pm, Rolf Camps wrote:
I'm afraid it's dangerous to encourage the use of '[]' as assignment to
a parameter in a function definition. If you use the function several
times 'default' always points to the same list.
On Dec 23, 7:10 am, alex23 wrote:
> On Dec 22, 6:51 pm, Rolf Camps wrote:
>
> > I'm afraid it's dangerous to encourage the use of '[]' as assignment to
> > a parameter in a function definition. If you use the function several
> > times 'default' always points to the same list.
>
> I appreciate th
On Dec 23, 3:22 pm, Ian Kelly wrote:
> Nobody is asking you to modify your coding style. The request is that
> you not throw it up as an example without mentioning the important
> caveats.
No, 100% no. It's not my responsibility to mention every potentially
relevant gotcha when providing example
On Thu, Dec 22, 2011 at 8:40 PM, alex23 wrote:
> On Dec 23, 12:59 pm, Ian Kelly wrote:
>> It's only irrelevant in the immediate context of the code you posted.
>> But when Joe Novice sees your code and likes it and duplicates it a
>> million times
>
> I'm sorry, but I'm not going to modify my cod
On Dec 21, 5:44 pm, Steven D'Aprano wrote:
> Yes, you should create your lists before trying to append to them.
>
> But you aren't forced to use a for-loop. You can use a list comprehension:
>
> x = [some_function(a) for a in range(n)]
>
> Notice that here you don't need x to pre-exist, because t
On Fri, Dec 23, 2011 at 2:40 PM, alex23 wrote:
> I'm sorry, but I'm not going to modify my coding style for the sake of
> bad programmers.
And there, folks, you have one of the eternal dilemmas. The correct
decision depends on myriad factors; if you're writing code to go into
the documentation as
On Dec 23, 12:59 pm, Ian Kelly wrote:
> It's only irrelevant in the immediate context of the code you posted.
> But when Joe Novice sees your code and likes it and duplicates it a
> million times
I'm sorry, but I'm not going to modify my coding style for the sake of
bad programmers.
The context
On Dec 21, 6:50 pm, alex23 wrote:
> On Dec 22, 8:25 am, Eric wrote:
>
> > This surprises me, can someone tell me why it shouldn't? I figure if
> > I want to create and initialize three scalars the just do "a=b=c=7",
> > for example, so why not extend it to arrays.
>
> The thing to remember is th
On Thu, Dec 22, 2011 at 7:10 PM, alex23 wrote:
> On Dec 22, 6:51 pm, Rolf Camps wrote:
>> I'm afraid it's dangerous to encourage the use of '[]' as assignment to
>> a parameter in a function definition. If you use the function several
>> times 'default' always points to the same list.
>
> I appre
On Dec 22, 6:51 pm, Rolf Camps wrote:
> I'm afraid it's dangerous to encourage the use of '[]' as assignment to
> a parameter in a function definition. If you use the function several
> times 'default' always points to the same list.
I appreciate the concern, but adding a default argument guard w
Rolf Camps wrote:
alex23 schreef op wo 21-12-2011 om 16:50 [-0800]:
I'd say that _is_ the most pythonic way, it's very obvious in its
intent (or would be with appropriate names). If it bothers you that
much:
def listgen(count, default=[]):
for _ in xrange(count):
yield d
alex23 schreef op wo 21-12-2011 om 16:50 [-0800]:
> On Dec 22, 8:25 am, Eric wrote:
> > This surprises me, can someone tell me why it shouldn't? I figure if
> > I want to create and initialize three scalars the just do "a=b=c=7",
> > for example, so why not extend it to arrays.
>
> The thing to
On Dec 22, 8:25 am, Eric wrote:
> This surprises me, can someone tell me why it shouldn't? I figure if
> I want to create and initialize three scalars the just do "a=b=c=7",
> for example, so why not extend it to arrays.
The thing to remember is that everything is an object, and that it's
better
On Wed, 21 Dec 2011 18:20:16 -0500, Dennis Lee Bieber wrote:
> For the amount of typing, it's easier to just do a straight line
> tuple unpack
>
a,b,c = ([],[],[])
Note that tuples are created by the comma, not the round brackets (or
parentheses for any Americans reading). So the rou
On Wed, 21 Dec 2011 14:25:17 -0800, Eric wrote:
> Is it true that if I want to create an array or arbitrary size such as:
>for a in range(n):
> x.append()
x is not defined, so you will get a NameError unless by some lucky fluke
something else has created x AND it happens to be a list.
On Wed, Dec 21, 2011 at 2:25 PM, Eric wrote:
>
> Is it true that if I want to create an array or arbitrary size such
> as:
> for a in range(n):
> x.append()
>
> I must do this instead?
> x=[]
> for a in range(n):
> x.append()
You can also use a list comprehension:
x = [ for a in
On 21 December 2011 22:25, Eric wrote:
> Is it true that if I want to create an array or arbitrary size such
> as:
> for a in range(n):
> x.append()
>
> I must do this instead?
> x=[]
> for a in range(n):
> x.append()
>
> Now to my actual question. I need to do the above for mult
Is it true that if I want to create an array or arbitrary size such
as:
for a in range(n):
x.append()
I must do this instead?
x=[]
for a in range(n):
x.append()
Now to my actual question. I need to do the above for multiple arrays
(all the same, arbitrary size). So I do thi
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