Python

keys problem

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Join Date: May 2008

Posts: 16

Reputation: eibwen is an unknown quantity at this point

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eibwen

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Newbie Poster

keys problem

Jun 6th, 2008

OK guys, I've hit a wall & can't find any info on what I'm wanting to do.
Maybe someone can help me out here or point me in the right direction please?

I have a shelve object- book.
If I do book.keys(), naturally I get a list of the keys- ['key1', 'key2', etc...]
When I do a book['key1'].keys(), I again get a list of those keys- ['keya', 'keyb', etc...]
Is there a way to find out which key a key belongs to?

like - keyb belongs to what key? (keyb belongs to key1)

Thanks

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Join Date: Jul 2006

Posts: 608

Reputation: jrcagle is on a distinguished road

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jrcagle

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Practically a Master Poster

Re: keys problem

Jun 6th, 2008

Well, that question may not have an answer if the values are not unique; for example, if

book['key1'] = {'keya':valuea, 'keyb':valueb}

and

book['key2'] = {'keya':valuec, 'keyd':valued}

then 'keya' cannot be mapped backwards.

But suppose that your values are unique. Then you could do this:

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 Python Syntax (Toggle Plain Text) 
>>> import shelve  ## set up an example
>>> f= shelve.open("mydatabase")
>>> f['one'] = {1:2,3:4}
>>> f['two'] = {5:6,7:8}
>>> f.close()
 
>>> revdict = {}  ## Here's the reverse lookup code
>>> for key in f.keys():
	for subkey in f[key]:
		revdict[subkey] = key
 
 
>>> revdict
{1: 'one', 3: 'one', 5: 'two', 7: 'two'}
>>> import shelve  ## set up an example
>>> f= shelve.open("mydatabase")
>>> f['one'] = {1:2,3:4}
>>> f['two'] = {5:6,7:8}
>>> f.close()

>>> revdict = {}  ## Here's the reverse lookup code
>>> for key in f.keys():
	for subkey in f[key]:
		revdict[subkey] = key

		
>>> revdict
{1: 'one', 3: 'one', 5: 'two', 7: 'two'}

Basically, you're just reversing a dictionary. But again, you must be mathematically certain that your values are unique; else, you'll clobber things.

Jeff