save dictionary to a file without brackets.

[Terry Reedy]

On 8/9/2012 5:21 PM, Tim Chase wrote:
> On 08/09/12 15:41, Roman Vashkevich wrote:
>> 10.08.2012, в 0:35, Tim Chase написал(а):
>>> On 08/09/12 15:22, Roman Vashkevich wrote:
>>>>> {(4, 5): 1, (5, 4): 1, (4, 4): 2, (2, 3): 1, (4, 3): 2}
>>>>> and i want to print to a file without the brackets comas and semicolon in order to obtain something like this?
>>>>> 4 5 1
>>>>> 5 4 1
>>>>> 4 4 2
>>>>> 2 3 1
>>>>> 4 3 2
>>>>
>>>> for key in dict:
>>>> 	print key[0], key[1], dict[key]
>>>
>>> This might read more cleanly with tuple unpacking:
>>>
>>>   for (edge1, edge2), cost in d.iteritems(): # or .items()
>>>     print edge1, edge2, cost
>>>
>>> (I'm making the assumption that this is a edge/cost graph...use
>>> appropriate names according to what they actually mean)
>>
>> dict.items() is a list - linear access time whereas with 'for
>> key in dict:' access time is constant:
>> http://python.net/~goodger/projects/pycon/2007/idiomatic/handout.html#use-in-where-possible-1
>
> That link doesn't actually discuss dict.{iter}items()
>
> Both are O(N) because you have to touch each item in the dict--you
> can't iterate over N entries in less than O(N) time.  For small
> data-sets, building the list and then iterating over it may be
> faster faster; for larger data-sets, the cost of building the list
> overshadows the (minor) overhead of a generator.  Either way, the
> iterate-and-fetch-the-associated-value of .items() & .iteritems()
> can (should?) be optimized in Python's internals to the point I
> wouldn't think twice about using the more readable version.

In 3.x, .keys, .values, and .items are set-like read-only views 
specifically designed for iteration. So in 3.x they are THE way to do so 
for whichever alternative is appropriate. Iterating by keys and then 
looking up values instead of yielding the values at the same time is 
extra work.

-- 
Terry Jan Reedy