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Subject: Re: save dictionary to a file without brackets.
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From: Roman Vashkevich <vashkevichrb@gmail.com>
In-Reply-To: <502429C3.5000600@tim.thechases.com>
Date: Fri, 10 Aug 2012 01:34:05 +0400
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References: <930ab3d8-4ab9-446d-9970-ee811eb70a44@googlegroups.com> <F1B463BB-19A6-4DB1-99B3-929CCBFB5920@gmail.com> <50241F14.2060209@tim.thechases.com> <36EA3847-6713-4C12-B47B-9B5E10325F00@gmail.com> <502429C3.5000600@tim.thechases.com>
To: Tim Chase <python.list@tim.thechases.com>
Cc: python-list@python.org, giuseppe.amatulli@gmail.com
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Xref: csiph.com comp.lang.python:26817

Actually, they are different.
Put a dict.{iter}items() in an O(k^N) algorithm and make it a hundred =
thousand entries, and you will feel the difference.
Dict uses hashing to get a value from the dict and this is why it's =
O(1).

10.08.2012, =D7 1:21, Tim Chase =CE=C1=D0=C9=D3=C1=CC(=C1):

> On 08/09/12 15:41, Roman Vashkevich wrote:
>> 10.08.2012, =D7 0:35, Tim Chase =CE=C1=D0=C9=D3=C1=CC(=C1):
>>> 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
>>>>=20
>>>> for key in dict:
>>>> 	print key[0], key[1], dict[key]
>>>=20
>>> This might read more cleanly with tuple unpacking:
>>>=20
>>> for (edge1, edge2), cost in d.iteritems(): # or .items()
>>>   print edge1, edge2, cost
>>>=20
>>> (I'm making the assumption that this is a edge/cost graph...use
>>> appropriate names according to what they actually mean)
>>=20
>> 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
>=20
> That link doesn't actually discuss dict.{iter}items()
>=20
> 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.
>=20
> -tkc
>=20
>=20