<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def search(self):
 """Search for a url by returning the value from the first callback that returns a non-None value"""


        for cb in SearchUrl.search_callbacks:

            try:
                v = cb(self)
                if v is not None:
                    return v
            except Exception as e:
                raise