Generate values for str.format style template strings from formatted output

Question

This might seem like a wierd requirement, but I am looking for a good implementation to do this.

I have a dict like

vals = dict(red='#F00', green='#0F0', blue='#00F')

and a string like

tpl = '{red}:{green}:{blue}'

and the str.formatted output

output = tpl.format(**vals)

All is well till here. However, I now need to do the reverse of this. I have to turn a string like '#F00:#0F0:#00F' into a dict of the values that we previously started with. Of course, I could just split and strip the string and take the values I need, but it will fail in the event the tpl string should change.

Any good ideas on how I can do this (If it can even be done, that is)?

Roshan Mathews · Accepted Answer · 2011-08-30 07:41:42Z

2

You can use regular expressions. (And maybe then you'll have two problems.)

>>> import re
>>> pattern = re.compile('(#[\da-fA-F]{3})')
>>> l = pattern.findall(output)
['#F00', '#0F0', '#00F']
>>> dict(zip(('red', 'green', 'blue'), l))
{'blue': '#00F', 'green': '#0F0', 'red': '#F00'}
>>>

answered Aug 30, 2011 at 7:41

Roshan Mathews

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5 Comments

sharat87 Over a year ago

+1 Nice and simple, me likes it :). Also, we do have two problems, the second being we now need a regex that matches the substitution strings correctly ;)

Roshan Mathews Over a year ago

You want something like parse('{red}:{green}:{blue}', '#F00:#0F0:#00F') that returns vals? That's more complicated, why don't you write out a solution and post it here, and it can be improved/fixed if required.

sharat87 Over a year ago

@rm, have been working on it for over a couple hours now. So far, its little more than doctests and a long undo history :)

sharat87 Over a year ago

But I am starting to doubt the possibility of such a thing now.

sharat87 Over a year ago

Yep, this is the best way we have :)

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