code: def verify_client_id(self):
          
  
          from .models import Client
          from .exceptions.invalid_client import ClientDoesNotExist
          from .exceptions.invalid_request import ClientNotProvided
  
          if self.client_id:
              try:
                  self.client = Client.objects.for_id(self.client_id)
              # Catching also ValueError for the case when client_id doesn't contain an integer.
              except (Client.DoesNotExist, ValueError):
                  raise ClientDoesNotExist()
          else:
              raise ClientNotProvided()
docs: Verify a provided client id against the database and set the `Client` object that is
          associated with it to `self.client`.
  
          TODO: Document all of the thrown exceptions.