def delete_breakpoint(self, bp):
        " remove breakpoint `bp'"
        bpnum = bp.number
        self.bpbynumber[bpnum] = None   # No longer in list
        index = (bp.filename, bp.line)
        if index not in self.bplist: return False
        self.bplist[index].remove(bp)
        if not self.bplist[index]:
            # No more breakpoints for this file:line combo
            del self.bplist[index]
        return True
remove breakpoint `bp