def bubble(self, o):
if o not in self._elements:<EOL><INDENT>raise ValueError('<STR_LIT>')<EOL><DEDENT>old = self._elements[:]<EOL>self.clear()<EOL>bubbles = []<EOL>for thiso in old:<EOL><INDENT>if thiso==o: bubbles.append(thiso)<EOL>else: self.push(thiso)<EOL><DEDENT>for thiso in bubbles:<EOL><INDENT>self.push(o)<EOL><DEDENT>return o<EOL>
raise *o* to the top of the stack and return *o*.  *o* must be
in the stack