gistfile1.py

def BranchWrapped(f, success, fail):
        try:
                r = f()
                print "success"
                success()
                return r
        except:
                fail()
                print "fail"

def ApplyStyle(w,s):
        w['style']=s
        print w['style']

...

                NormalStyle = lambda w: ApplyStyle(w,'TEntry')
                InvalidStyle = lambda w: ApplyStyle(w, 'Invalid.TEntry')
                inv = lambda x: InvalidStyle(x)
                val = lambda x: NormalStyle(x)

                self._bGridEntry = Entry(batteryFrame)
                self._bGridEntry.grid(row=3,column=1,sticky="WE")
                self._bGrid = StringVar()
                self._bGridEntry["textvariable"] = self._bGrid
                self._bGrid.trace("w",lambda n,i,m : BranchWrapped(f,partial(val, x=self._bGridEntry),partial(inv, x=self._bGridEntry)))