code: def add_proxy(self, proxy):
          
          protocol = proxy.protocol
          addr = proxy.addr
          if addr in self.proxies:
              self.proxies[protocol][addr].last_checked = proxy.last_checked
          else:
              self.proxies[protocol][addr] = proxy
              self.addr_list[protocol].append(addr)
docs: Add a valid proxy into pool
  
          You must call `add_proxy` method to add a proxy into pool instead of
          directly operate the `proxies` variable.