code: def assignUserCredits(self, usernames, credits):
          
          userAssignments = []
          for name in usernames:
              userAssignments.append(
                  {
                      "username" : name,
                      "credits" : credits
                  }
              )
          params = {
              "userAssignments" : userAssignments,
              "f" : "json"
          }
          url = self.root + "/assignUserCredits"
          return self._post(url=url,
                               param_dict=params,
                               securityHandler=self._securityHandler,
                               proxy_url=self._proxy_url,
                               proxy_port=self._proxy_port)
docs: assigns credit to a user.
          Inputs:
             usernames - list of users
             credits - number of credits to assign to the users
          Ouput:
             dictionary