'Writes the difference between b4 and after to self.stderr.
The data is dictionaries returned from
:meth:`get_resource_usage`.'

def display_timing(self, b4, after):

    v = list(b4.keys())
    for i in after:
        if (i not in v):
            v.append(i)
    v.sort()
    for k in v:
        if ((k in b4) and (k in after)):
            one = b4[k]
            two = after[k]
            val = (two - one)
            if val:
                if (type(val) == float):
                    self.write(self.stderr, ('+    %s:    %.4f\n' % (k, val)))
                else:
                    self.write(self.stderr, ('+    %s:    %d\n' % (k, val)))
