Recursive update of arbitrarily nested dicts

[maxm]

I am writing a module where I am updating nested dicts, and it has this
method:

    def addDayToTrack(self, trackId, year, theDay, day):
        if not self.tracks.has_key(trackId):
            self.tracks.update({trackId:{year:{theDay:day}}})
        elif not self.tracks[trackId].has_key(year):
            self.tracks[trackId].update({year:{theDay:day}})
        elif not self.tracks[trackId][year].has_key(theDay):
            self.tracks[trackId][year][theDay] = day

oh and self.tracks={}

But clearly this could be solved more generally by a recursive function.
Something like:

def addDayToTrack(self, trackId, year, theDay, day):
    # recursive update
    self.rUpdate(self.tracks, {trackId:{year:{theDay:day}}})

Now my only problem is that recursive method "rUpdate(targetDict,
itemDict)".

Knowing this group, many other has written a method like this before me.
Does anybody have one at hand?

The idea is that it should traverse the targetDict, updating keys and values
as apropriate.

Anyhoo ... I will try it myself, but recursion is not my pot of tea though.

regards Max M