Re: [Tutor] Iterating a dict with an iteration counter? How would *you* do it?

2013-02-05 Thread Oscar Benjamin 
On 5 February 2013 03:56, eryksun eryk...@gmail.com wrote:
 On Mon, Feb 4, 2013 at 7:04 PM, Dave Angel da...@davea.name wrote:
 Nope, in both Python 2 and 3 iterating over a dict directly just
 provides the key. That's also how if key in dict works.

 A dict implements __contains__ for an efficient in test. In general,
 the interpreter falls back to using iteration if a type lacks
 __contains__.

I almost wrote this response but then I realised that Dave probably
meant that obj in dict returns True if the dict has a key equal to
obj rather than if the dict has a (key, value) pair equal to obj.


Oscar
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Re: [Tutor] Iterating a dict with an iteration counter? How would *you* do it?

2013-02-05 Thread eryksun 
On Tue, Feb 5, 2013 at 6:27 AM, Oscar Benjamin
oscar.j.benja...@gmail.com wrote:

 I almost wrote this response but then I realised that Dave probably
 meant that obj in dict returns True if the dict has a key equal to
 obj rather than if the dict has a (key, value) pair equal to obj.

Thanks, that's probably what Steven meant. It's keeping item in
a_dict consistent with item in list(a_dict).
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Re: [Tutor] Iterating a dict with an iteration counter? How would *you* do it?

2013-02-05 Thread Steven D'Aprano 

On 05/02/13 22:27, Oscar Benjamin wrote:

On 5 February 2013 03:56, eryksuneryk...@gmail.com  wrote:

On Mon, Feb 4, 2013 at 7:04 PM, Dave Angelda...@davea.name  wrote:

Nope, in both Python 2 and 3 iterating over a dict directly just
provides the key. That's also how if key in dict works.


A dict implements __contains__ for an efficient in test. In general,
the interpreter falls back to using iteration if a type lacks
__contains__.


I almost wrote this response but then I realised that Dave probably
meant that obj in dict returns True if the dict has a key equal to
obj rather than if the dict has a (key, value) pair equal to obj.



It was actually me, not Dave, and yes, that's what I meant. I didn't mean
that dict containment tests were literally implemented by iterating over
the keys checking each one in turn, since that would be horribly
inefficient for something so critical as a dict. Although I can see why
eryksun may have thought so, sorry for any confusion caused by my poor
wording.

Although note that Python does fallback on iteration for containment if
you don't define a __contains__ method:


py class Test(object):
... def __getitem__(self, n):
... if n = 5: raise IndexError
... return n + 100
...
py t = Test()
py 3 in t
False
py 103 in t
True



--
Steven
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[Tutor] Iterating a dict with an iteration counter? How would *you* do it?

2013-02-04 Thread Modulok 
List,

Simple question: Is there a common pattern for iterating a dict, but also
providing access to an iteration counter? Here's what I usually do (below). I'm
just wondering if there are other, more clever ways::

data = {'a': apple, 'b': banana, 'c': cherry}
i = 0
for k,v in data.items():
print(i: %s, k: %s, v: %s % (i,k,v))
i += 1

Another variant, same idea::

data = {'a': apple, 'b': banana, 'c': cherry}
for i,k,v in zip(range(len(data)), data.keys(), data.values()):
print(i: %s, k: %s, v: %s % (i,k,v))


How would you do it?
-Modulok-
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Re: [Tutor] Iterating a dict with an iteration counter? How would *you* do it?

2013-02-04 Thread Dave Angel 

On 02/04/2013 12:13 PM, Modulok wrote:

List,

Simple question: Is there a common pattern for iterating a dict, but also
providing access to an iteration counter? Here's what I usually do (below). I'm
just wondering if there are other, more clever ways::

 data = {'a': apple, 'b': banana, 'c': cherry}
 i = 0
 for k,v in data.items():
 print(i: %s, k: %s, v: %s % (i,k,v))
 i += 1

Another variant, same idea::

 data = {'a': apple, 'b': banana, 'c': cherry}
 for i,k,v in zip(range(len(data)), data.keys(), data.values()):
 print(i: %s, k: %s, v: %s % (i,k,v))


How would you do it?
-Modulok-


enumerate()


for i, (k, v) in enumerate(data.items()):

--
DaveA
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Re: [Tutor] Iterating a dict with an iteration counter? How would *you* do it?

2013-02-04 Thread Modulok 
Hmm.. no kidding. Well, at least I knew I was over-complicating it.

Cheers!
-Modulok-


On 2/4/13, Dave Angel da...@davea.name wrote:
 On 02/04/2013 12:13 PM, Modulok wrote:
 List,

 Simple question: Is there a common pattern for iterating a dict, but also
 providing access to an iteration counter? Here's what I usually do
 (below). I'm
 just wondering if there are other, more clever ways::

  data = {'a': apple, 'b': banana, 'c': cherry}
  i = 0
  for k,v in data.items():
  print(i: %s, k: %s, v: %s % (i,k,v))
  i += 1

 Another variant, same idea::

  data = {'a': apple, 'b': banana, 'c': cherry}
  for i,k,v in zip(range(len(data)), data.keys(), data.values()):
  print(i: %s, k: %s, v: %s % (i,k,v))


 How would you do it?
 -Modulok-

 enumerate()


 for i, (k, v) in enumerate(data.items()):

 --
 DaveA
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Re: [Tutor] Iterating a dict with an iteration counter? How would *you* do it?

2013-02-04 Thread Dave Angel 

On 02/04/2013 12:58 PM, Modulok wrote:

Hmm.. no kidding. Well, at least I knew I was over-complicating it.

Cheers!
-Modulok-



Please don't top-post.

Another point.  I don't currently have Python 3.x installed, but I seem 
to remember that in Python 3 you can use the dict itself as an iterator 
providing both key and value.  If I'm right, then it could be simplified 
further to:



for i, (k, v) in enumerate(data):

A simple test will prove me right or wrong.


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DaveA
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Re: [Tutor] Iterating a dict with an iteration counter? How would *you* do it?

2013-02-04 Thread Steven D'Aprano 

On 05/02/13 09:26, Dave Angel wrote:


Another point. I don't currently have Python 3.x installed, but I seem to
remember that in Python 3 you can use the dict itself as an iterator
providing both key and value. If I'm right, then it could be simplified
further to:


for i, (k, v) in enumerate(data):


Nope, in both Python 2 and 3 iterating over a dict directly just provides the
key. That's also how if key in dict works.



--
Steven
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Re: [Tutor] Iterating a dict with an iteration counter? How would *you* do it?

2013-02-04 Thread Dave Angel 

On 02/04/2013 06:18 PM, Steven D'Aprano wrote:

On 05/02/13 09:26, Dave Angel wrote:


Another point. I don't currently have Python 3.x installed, but I seem to
remember that in Python 3 you can use the dict itself as an iterator
providing both key and value. If I'm right, then it could be simplified
further to:


for i, (k, v) in enumerate(data):


Nope, in both Python 2 and 3 iterating over a dict directly just
provides the
key. That's also how if key in dict works.



Then I'm glad I was tentative about it.  I do recall there was some 
difference.  Was it just that items(), keys() and values() methods 
return a view (iterator) instead of a list, and the iter*() versions are 
gone?


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DaveA
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Re: [Tutor] Iterating a dict with an iteration counter? How would *you* do it?

2013-02-04 Thread eryksun 
On Mon, Feb 4, 2013 at 7:04 PM, Dave Angel da...@davea.name wrote:
 Nope, in both Python 2 and 3 iterating over a dict directly just
 provides the key. That's also how if key in dict works.

A dict implements __contains__ for an efficient in test. In general,
the interpreter falls back to using iteration if a type lacks
__contains__.

In 2.x iter(some_dict) returns a dictionary-keyiterator (weird
hyphen). In 3.x it's a dict_keyiterator (normal underscore).

 Was it just that items(), keys() and values() methods return a view
 (iterator) instead of a list, and the iter*() versions are gone?

In 3.x, keys() and items() return views that are iterable (__iter__)
and that implement the sequence methods __len__ and __contains__ as
well as a few set operations that return a set: intersection (),
union (|), difference (-), and symmetric difference (^). Using the set
methods for items() requires the values to also be hashable. The view
returned by values() doesn't bother implementing __contains__ and the
set operations, but it does have __iter__ and __len__. 2.7 provides
these views via viewkeys(), viewitems(), and viewvalues().

The corresponding iterators returned by iter() in 3.x are
dict_keyiterator, dict_itemiterator, and dict_valueiterator.
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