'inverting' a dict

[anton muhin]

Irmen de Jong wrote:
> Hi
> I have this dict that maps a name to a sequence of other names.
> I want to have it reversed, i.e., map the other names each to
> the key they belong to (yes, the other names are unique and
> they only occur once). Like this:
> 
> { "key1": ("value1", "value2"), "key2": ("value3,) }
> 
> -->
> 
> { "value1": "key1", "value2": "key1", "value3": "key2" }
> 
> What I'm doing is using a nested loop:
> 
> dict2={}
> for (key,value) in dict1.items():
>     for name in value:
>         dict2[name] = key
> 
> which is simple enough, but I'm hearing this little voice in
> the back of my head saying "there's a simpler solution".
> Is there? What is it? ;-)
> 
> Thanks
> --Irmen.
> 

It's seems like rather nice Python for me ;). Two more variants:

inverted = {}
for k, vs in d.iteritems():
     inverted.update(dict([(v, k) for v in vs]))

map(
    lambda (k, vs): inverted.update(dict([(v, k) for v in vs])),
    d.iteritems()
)

happy new year,
anton.