'inverting' a dict

[Nick Vargish]

Irmen de Jong <irmen at -NOSPAM-REMOVETHIS-xs4all.nl> writes:

> 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:

That's almost spooky, I'm working on a project for which I needed
something like this. I've just read the entire thread and my solution
seems pretty naive:

def invertdict(d):
    """Returns a dict whose key-value pairs are the value-key pairs of d."""
    ret = {}
    for k in d:
        ret[d[k]] = k
    return ret

I only need to do it once or twice, at program start-up, so time-
efficiency wasn't a critical factor. I'm guessing the list
comprehension tactics are faster, though.

Sorry about being late to the party, I've been away from Usenet for
about three weeks...

Nick

-- 
#  sigmask  ||  0.2  ||  20030107  ||  public domain  ||  feed this to a python
print reduce(lambda x,y:x+chr(ord(y)-1),' Ojdl!Wbshjti!=obwAcboefstobudi/psh?')