Concise idiom to initialize dictionaries

[Frohnhofer, James]

My initial problem was to initialize a bunch of dictionaries at the start of a
function.

I did not want to do
def fn():
	a = {}
	b = {}
	c = {}
	. . .
	z = {}
simply because it was ugly and wasted screen space.

First I tried:

	for x in (a,b,c,d,e,f,g): x = {}

which didn't work (but frankly I didn't really expect it to.)
Then I tried:

	for x in ('a','b','c','d','e','f','g'): locals()[x]={}

which did what I wanted, in the interpreter.  When I put it inside a function,
it doesn't seem to work.  If I print locals() from inside the function, I can
see them, and they appear to be fine, but the first time I try to access one
of them I get a "NameError: global name 'a' is not defined"

Now obviously I could easily avoid this problem by just initializing each
dictionary, but is there something wrong about my understanding of locals,
that my function isn't behaving the way I expect?



> -----Original Message-----
> From: python-list-bounces+james.frohnhofer=csfb.com at python.org
> [mailto:python-list-bounces+james.frohnhofer=csfb.com at python.org]On
> Behalf Of Dennis Lee Bieber
> Sent: Tuesday, November 09, 2004 10:31 AM
> To: python-list at python.org
> Subject: Re: Determining combination of bits
> 
> 
> On Mon, 8 Nov 2004 21:18:36 -0800, "news.west.cox.net"
> <sean.berry2 at cox.net> declaimed the following in comp.lang.python:
> 
> > > Note: 2^1 = 2, so your dictionary is already in error...
> > >
> > 
> > The dictionary was filled with arbitrary values, not
> > { x : 2^x } values like you might have thought.
> 
> 	Well, you had stated "powers of two"... If all you wanted is a
> bit mapping you could probably drop the dictionary and just use a list
> of the values, indexed by the bit position, and my first attempt
> logic...
> 
> > 
> > It is actually more like {1:123, 2:664, 4:323, 8:990, 16:221... etc}
> > 
> > 
> 
> CheckBoxes = [ "FirstChoice",
>                "SecondChoice",
>                "ThirdChoice",
>                "FourthChoice",
>                "FifthChoice",
>                "SixthChoice" ]
> 
> 
> for num in [22, 25, 9]:
>     bit = 0
>     while num:
>         if num & 1:
>             print CheckBoxes[bit],
>         bit = bit + 1
>         num = num >> 1
>     print
> 
> SecondChoice ThirdChoice FifthChoice
> FirstChoice FourthChoice FifthChoice
> FirstChoice FourthChoice
> 
> where "num" is the sum of the checkbox index values (or whatever
> selection mechanism is used), assuming /they/ were set up in 2^(n+1)
> scheme (n = bit position, starting with 0)...
> 
> -- 
>  > ============================================================== <
>  >   wlfraed at ix.netcom.com  | Wulfraed  Dennis Lee Bieber  KD6MOG <
>  >      wulfraed at dm.net     |       Bestiaria Support Staff       <
>  > ============================================================== <
>  >           Home Page: <http://www.dm.net/~wulfraed/>            <
>  >        Overflow Page: <http://wlfraed.home.netcom.com/>        <
> -- 
> http://mail.python.org/mailman/listinfo/python-list
> 

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