Re: Python 3: dict & dict.keys()

On 7/25/2013 12:21 PM, Ethan Furman wrote: On 07/25/2013 09:11 AM, Prasad, Ramit wrote: Hmm, that is a change that makes some sense to me. Does the view get updated when dictionary changes or is a new view needed? I assume the latter. Nope, the former. That is a big advantage that the views

Re: Python 3: dict & dict.keys()

On 07/25/2013 09:11 AM, Prasad, Ramit wrote: Terry Reedy wrote: On 7/24/2013 4:34 PM, Prasad, Ramit wrote: I am still not clear on the advantage of views vs. iterators. A1: Views are iterables that can be iterated more than once. Therefore, they can be passed to a function that re-iterates

Re: Python 3: dict & dict.keys()

Ian Kelly wrote: > On Thu, Jul 25, 2013 at 2:13 AM, Peter Otten <__pete...@web.de> wrote: >> Chris Angelico wrote: >> >>> On Thu, Jul 25, 2013 at 5:04 PM, Steven D'Aprano >>> wrote: - Views support efficient (O(1) in the case of keys) membership testing, which neither iterkeys() nor Pyt

RE: Python 3: dict & dict.keys()

Terry Reedy wrote: > > On 7/24/2013 4:34 PM, Prasad, Ramit wrote: > > > I am still not clear on the advantage of views vs. iterators. > > A1: Views are iterables that can be iterated more than once. Therefore, > they can be passed to a function that re-iterates its inputs, or to > multiple funct

Re: Python 3: dict & dict.keys()

On Thu, Jul 25, 2013 at 2:13 AM, Peter Otten <__pete...@web.de> wrote: > Chris Angelico wrote: > >> On Thu, Jul 25, 2013 at 5:04 PM, Steven D'Aprano >> wrote: >>> - Views support efficient (O(1) in the case of keys) membership testing, >>> which neither iterkeys() nor Python2 keys() does. >> >> To

Re: Python 3: dict & dict.keys()

On Fri, Jul 26, 2013 at 12:57 AM, Steven D'Aprano wrote: > [ snip lengthy explanation of sets ] > The union operator ought to > be symmetrical, a ∪ b should be identical to b ∪ a, but isn't. Another > leaky abstraction. Right. I agree with all your theory, which is fine and good. If we had a "set

Re: Python 3: dict & dict.keys()

On Thu, 25 Jul 2013 20:34:23 +1000, Chris Angelico wrote: > On Thu, Jul 25, 2013 at 7:44 PM, Steven D'Aprano > wrote: >> On Thu, 25 Jul 2013 18:15:22 +1000, Chris Angelico wrote: >>> That's true, but we already have that issue with sets. What's the >>> union of {0} and {0.0}? Python's answer: It

Re: Python 3: dict & dict.keys()

On 07/24/2013 10:48 PM, Steven D'Aprano wrote: On Wed, 24 Jul 2013 08:57:11 -0700, Ethan Furman wrote: My point is that in 2.x .keys() did something different from the dict, while in 3.x it appears to me that they are the same. Then you aren't looking very closely. Actually, I am. That's w

Re: Python 3: dict & dict.keys()

On 07/24/2013 11:01 PM, alex23 wrote: On 25/07/2013 4:31 AM, Ethan Furman wrote: 2) Hopefully learn something about when a view is useful. I haven't seeen this mentioned - forgive me if it's a repeat - but views are constant references to whichever set they represent. Python 2.7: dd = d

Re: Python 3: dict & dict.keys()

On 25.07.2013 07:48, Steven D'Aprano wrote: > Then you aren't looking very closely. d.keys() returns a set-like view > into the dict, which is great for comparing elements: > > py> d1 = dict.fromkeys([1, 2, 3, 4]) > py> d2 = dict.fromkeys([3, 4, 5, 6]) > py> d1.keys() & d2.keys() # keys that ar

Re: Python 3: dict & dict.keys()

On Thu, Jul 25, 2013 at 7:44 PM, Steven D'Aprano wrote: > On Thu, 25 Jul 2013 18:15:22 +1000, Chris Angelico wrote: >> That's true, but we already have that issue with sets. What's the union >> of {0} and {0.0}? Python's answer: It depends on the order of the >> operands. > > That's a side-effect

Re: Python 3: dict & dict.keys()

On Thu, 25 Jul 2013 18:15:22 +1000, Chris Angelico wrote: > On Thu, Jul 25, 2013 at 5:27 PM, Steven D'Aprano > wrote: >> On Thu, 25 Jul 2013 16:02:42 +1000, Chris Angelico wrote: >> >>> On Thu, Jul 25, 2013 at 3:48 PM, Steven D'Aprano >>> wrote: Dicts aren't sets, and don't support set meth

Re: Python 3: dict & dict.keys()

On Thu, Jul 25, 2013 at 5:27 PM, Steven D'Aprano wrote: > On Thu, 25 Jul 2013 16:02:42 +1000, Chris Angelico wrote: > >> On Thu, Jul 25, 2013 at 3:48 PM, Steven D'Aprano >> wrote: >>> Dicts aren't sets, and don't support set methods: >>> >>> py> d1 - d2 >>> Traceback (most recent call last): >>>

Re: Python 3: dict & dict.keys()

Chris Angelico wrote: > On Thu, Jul 25, 2013 at 5:04 PM, Steven D'Aprano > wrote: >> - Views support efficient (O(1) in the case of keys) membership testing, >> which neither iterkeys() nor Python2 keys() does. > > To save me the trouble and potential error of digging through the > source code:

Re: Python 3: dict & dict.keys()

On Thu, Jul 25, 2013 at 5:04 PM, Steven D'Aprano wrote: > - Views support efficient (O(1) in the case of keys) membership testing, > which neither iterkeys() nor Python2 keys() does. To save me the trouble and potential error of digging through the source code: What's the complexity of membership

Re: Python 3: dict & dict.keys()

On Thu, 25 Jul 2013 16:02:42 +1000, Chris Angelico wrote: > On Thu, Jul 25, 2013 at 3:48 PM, Steven D'Aprano > wrote: >> Dicts aren't sets, and don't support set methods: >> >> py> d1 - d2 >> Traceback (most recent call last): >> File "", line 1, in >> TypeError: unsupported operand type(s) fo

Re: Python 3: dict & dict.keys()

On Wed, 24 Jul 2013 11:31:58 -0700, Ethan Furman wrote: > On 07/24/2013 10:23 AM, Stefan Behnel wrote: >> Peter Otten, 24.07.2013 08:23: >>> Ethan Furman wrote: So, my question boils down to: in Python 3 how is dict.keys() different from dict? What are the use cases? >>> >>> To me

Re: Python 3: dict & dict.keys()

On 25/07/2013 4:31 AM, Ethan Furman wrote: 2) Hopefully learn something about when a view is useful. I haven't seeen this mentioned - forgive me if it's a repeat - but views are constant references to whichever set they represent. Python 2.7: >>> dd = dict(a=1,b=2,c=3) >>> keys = dd.keys

Re: Python 3: dict & dict.keys()

On Thu, Jul 25, 2013 at 3:48 PM, Steven D'Aprano wrote: > Dicts aren't sets, and don't support set methods: > > py> d1 - d2 > Traceback (most recent call last): > File "", line 1, in > TypeError: unsupported operand type(s) for -: 'dict' and 'dict' I wouldn't take this as particularly signific

Re: Python 3: dict & dict.keys()

On Wed, 24 Jul 2013 17:59:43 -0700, Ethan Furman wrote: >> Repeat after me: "In Python 2, d.keys() returns a list of keys, so if I >> want a list of keys in Python 3, call list explicitly list(d.keys())." > > Actually, I would recommend `list(d)`, which also works the same in both > 2 and 3. Fai

Re: Python 3: dict & dict.keys()

On Wed, 24 Jul 2013 13:17:12 -0400, Terry Reedy wrote: > On 7/24/2013 12:34 PM, Chris Angelico wrote: > >> Side point: Why is iterating over a dict equivalent to .keys() rather >> than .items()? It feels odd that, with both options viable, the >> implicit version iterates over half the dict inste

Re: Python 3: dict & dict.keys()

On Wed, 24 Jul 2013 08:57:11 -0700, Ethan Furman wrote: > My point is that in 2.x .keys() did something different from the dict, > while in 3.x it appears to me that they are the same. Then you aren't looking very closely. d.keys() returns a set-like view into the dict, which is great for compar

Re: Python 3: dict & dict.keys()

Ethan Furman writes: > On 07/23/2013 07:11 PM, Steven D'Aprano wrote: > > On Tue, 23 Jul 2013 18:16:08 -0700, Ethan Furman wrote: > >> And everything I thought I knew about when to use one or the other went > >> out the window. > > > > Surely not. The fundamental behaviour of Python's data model

Re: Python 3: dict & dict.keys()

On 07/23/2013 07:11 PM, Steven D'Aprano wrote: On Tue, 23 Jul 2013 18:16:08 -0700, Ethan Furman wrote: So now, in Python 3, .keys(), .values(), even .items() all return these 'view' thingies. And everything I thought I knew about when to use one or the other went out the window. Surely not.

Re: Python 3: dict & dict.keys()

On 07/24/2013 01:34 PM, Prasad, Ramit wrote: I am still not clear on the advantage of views vs. iterators. What makes d.viewkeys() better than d.iterkeys()? Why did they decide not to rename d.iterkeys() to d.keys() and instead use d.viewkeys()? Is the iteration over a set operation on keys real

Re: Python 3: dict & dict.keys()

On 7/24/2013 4:34 PM, Prasad, Ramit wrote: I am still not clear on the advantage of views vs. iterators. A1: Views are iterables that can be iterated more than once. Therefore, they can be passed to a function that re-iterates its inputs, or to multiple functions. They support 'x in view' as

Re: Python 3: dict & dict.keys()

Am 24.07.2013 18:34, schrieb Chris Angelico: > Side point: Why is iterating over a dict equivalent to .keys() rather > than .items()? It feels odd that, with both options viable, the > implicit version iterates over half the dict instead of all of it. > Obviously it can't be changed now, even if .i

RE: Python 3: dict & dict.keys()

Stefan Behnel wrote: > Ethan Furman, 24.07.2013 20:31: > > On 07/24/2013 10:23 AM, Stefan Behnel wrote: > >> Peter Otten, 24.07.2013 08:23: > >>> Ethan Furman wrote: > > So, my question boils down to: in Python 3 how is dict.keys() different > from dict? What are the use cases? > >

Re: Python 3: dict & dict.keys()

On 07/24/2013 12:59 PM, Stefan Behnel wrote: I think the question is: how else would you implement an interface that doesn't restrict itself to returning a list? I mean, previously, the following was totally inefficient in terms of memory: value in d.values() It now avoids creating an int

Re: Python 3: dict & dict.keys()

Ethan Furman, 24.07.2013 20:31: > On 07/24/2013 10:23 AM, Stefan Behnel wrote: >> Peter Otten, 24.07.2013 08:23: >>> Ethan Furman wrote: So, my question boils down to: in Python 3 how is dict.keys() different from dict? What are the use cases? >>> >>> To me it looks like views are

Re: Python 3: dict & dict.keys()

On 07/24/2013 10:23 AM, Stefan Behnel wrote: Peter Otten, 24.07.2013 08:23: Ethan Furman wrote: So, my question boils down to: in Python 3 how is dict.keys() different from dict? What are the use cases? To me it looks like views are a solution waiting for a problem. They reduce the API o

Re: Python 3: dict & dict.keys()

On Thu, Jul 25, 2013 at 3:17 AM, Terry Reedy wrote: > On 7/24/2013 12:34 PM, Chris Angelico wrote: > >> Side point: Why is iterating over a dict equivalent to .keys() rather >> than .items()? It feels odd that, with both options viable, the >> implicit version iterates over half the dict instead o

Re: Python 3: dict & dict.keys()

Peter Otten, 24.07.2013 08:23: > Ethan Furman wrote: >> So, my question boils down to: in Python 3 how is dict.keys() different >> from dict? What are the use cases? > > I just grepped through /usr/lib/python3, and could not identify a single > line where some_object.keys() wasn't either wrappe

Re: Python 3: dict & dict.keys()

Chris Angelico, 24.07.2013 18:34: > On Thu, Jul 25, 2013 at 1:57 AM, Ethan Furman wrote: >> On 07/24/2013 05:51 AM, Oscar Benjamin wrote: >>> What do you mean? Why would you want to create a temporary list just to >>> iterate over it explicitly or implicitly (set, >>> sorted, max,...)? >> >> You wo

Re: Python 3: dict & dict.keys()

On 7/24/2013 12:34 PM, Chris Angelico wrote: Side point: Why is iterating over a dict equivalent to .keys() rather than .items()? It feels odd that, with both options viable, the implicit version iterates over half the dict instead of all of it. Obviously it can't be changed now, even if .items(

Re: Python 3: dict & dict.keys()

On Thu, Jul 25, 2013 at 1:57 AM, Ethan Furman wrote: > On 07/24/2013 05:51 AM, Oscar Benjamin wrote: >> What do you mean? Why would you want to create a temporary list just to >> iterate over it explicitly or implicitly (set, >> sorted, max,...)? > > You wouldn't. But you don't need .keys() for t

Re: Python 3: dict & dict.keys()

On Jul 24, 2013 2:27 PM, "Peter Otten" <__pete...@web.de> wrote: > > Oscar Benjamin wrote: > > > On Jul 24, 2013 7:25 AM, "Peter Otten" <__pete...@web.de> wrote: > >> > >> Ethan Furman wrote: > >> > >> > So, my question boils down to: in Python 3 how is dict.keys() > >> > different > >> > from dic

Re: Python 3: dict & dict.keys()

On 07/24/2013 05:51 AM, Oscar Benjamin wrote: On Jul 24, 2013 7:25 AM, "Peter Otten" <__pete...@web.de > wrote: Ethan Furman wrote: > So, my question boils down to: in Python 3 how is dict.keys() different > from dict? What are the use cases? I just grepped through

Re: Python 3: dict & dict.keys()

On Wed, Jul 24, 2013 at 8:58 AM, Skip Montanaro wrote: >> What do you mean? Why would you want to create a temporary list just to >> iterate over it explicitly or implicitly (set, sorted, max,...)? > > Because while iterating over the keys, he might also want to add or > delete keys to/from the di

Re: Python 3: dict & dict.keys()

On Tue, Jul 23, 2013 at 8:11 PM, Steven D'Aprano wrote: > Basically, views are set-like, not list-like. The keys and items views are set-like. The values view is not. -- http://mail.python.org/mailman/listinfo/python-list

Re: Python 3: dict & dict.keys()

> What do you mean? Why would you want to create a temporary list just to > iterate over it explicitly or implicitly (set, sorted, max,...)? Because while iterating over the keys, he might also want to add or delete keys to/from the dict. You can't do that while iterating over them in-place. Thi

Re: Python 3: dict & dict.keys()

Oscar Benjamin wrote: > On Jul 24, 2013 7:25 AM, "Peter Otten" <__pete...@web.de> wrote: >> >> Ethan Furman wrote: >> >> > So, my question boils down to: in Python 3 how is dict.keys() >> > different >> > from dict? What are the use cases? >> >> I just grepped through /usr/lib/python3, and could

Re: Python 3: dict & dict.keys()

On 2013-07-24, Peter Otten <__pete...@web.de> wrote: >> So, my question boils down to: in Python 3 how is dict.keys() >> different from dict? What are the use cases? > > I just grepped through /usr/lib/python3, and could not identify > a single line where some_object.keys() wasn't either wrapped

Re: Python 3: dict & dict.keys()

On Jul 24, 2013 7:25 AM, "Peter Otten" <__pete...@web.de> wrote: > > Ethan Furman wrote: > > > So, my question boils down to: in Python 3 how is dict.keys() different > > from dict? What are the use cases? > > I just grepped through /usr/lib/python3, and could not identify a single > line where s

Re: Python 3: dict & dict.keys()

Ethan Furman wrote: > So, my question boils down to: in Python 3 how is dict.keys() different > from dict? What are the use cases? I just grepped through /usr/lib/python3, and could not identify a single line where some_object.keys() wasn't either wrapped in a list (or set, sorted, max) call,

Re: Python 3: dict & dict.keys()

On Tue, 23 Jul 2013 18:16:08 -0700, Ethan Furman wrote: > Back in Python 2.x days I had a good grip on dict and dict.keys(), and > when to use one or the other. > > Then Python 3 came on the scene with these things called 'views', and > while range couldn't be bothered, dict jumped up and down sh