How can I create a dict that sets a flag if it's been modified

[Brian van den Broek]

Brian van den Broek said unto the world upon 12/01/06 03:42 AM:
> sandravandale at yahoo.com said unto the world upon 12/01/06 03:15 AM:
> 
>>I can think of several messy ways of making a dict that sets a flag if
>>it's been altered, but I have a hunch that experienced python
>>programmers would probably have an easier (well maybe more Pythonic)
>>way of doing this.

<snip>

> here's one attempt. (I'm no expert, so wait for better :-)
> 
>  >>> class ModFlagDict(dict):
> 	def __init__(self, *args, **kwargs):
> 		super(ModFlagDict, self).__init__(*args, **kwargs)
> 		self.modified = False
> 	def __setitem__(self, key, value):
> 		self.modified = True
> 		super(ModFlagDict, self).__setitem__(key, value)

<snip>

> It's broken in at least one way:
> 
>  >>> newmd = ModFlagDict(3=4, 1=5)
> SyntaxError: keyword can't be an expression
>  >>>
> 
> So, as it stands, no integers, floats, tuples, etc can be keys on 
> initialization. I think that can be be worked around by catching the 
> exceptions and setting the desired key-value pairs that way. But, it 
> is almost 4am, and I also suspect there is a much better way I am not 
> thinking of :-)

Sorry for the self-reply, but I just realized my original code isn't 
quite so bad as:

# class ModFlagDict as before

 >>> mdict = ModFlagDict({42:"This will work", (7, 6):"Python comes 
through, again!"})
 >>> mdict
{42: 'This will work', (7, 6): 'Python comes through, again!'}
 >>> mdict.modified
False
 >>> mdict[42]=":-)"
 >>> mdict
{42: ':-)', (7, 6): 'Python comes through, again!'}
 >>> mdict.modified
True
 >>>

I'll wager someone will point out a better way still, though.

Best,

Brian vdB