A dedicated TaggingService exists in moto.utilities, to help with storing/retrieving tags for resources.
Not all services use it yet, but contributors are encouraged to use the TaggingService for all new features.
When requesting a list of resources, almost all AWS services use pagination to stagger the response. Moto provides a utility class to automatically paginate a response, without having to manually write the logic.
There are three components that make this work:
- The Responses-method will call the backend with a max_result/next_token parameter
- The backend-method has a plain method that's decorated with @paginate
- A configuration model is supplied to the decorator that contains all the details.
See the below example how it works in practice:
python
class MyResponse(BaseResponse):
# The Response-class looks like any other - read the input parameters, and call the backend to retrieve the resources def list_resources(): max_results = 100 next_token = self._get_param("NextToken") # Note that we're getting both the results and the next_token # The decorator in the backend returns this tuple paged_results, next_token = self.backend.list_resources( max_results=max_results, next_token=next_token ) ...
from moto.utilities.paginator import paginate class MyBackend(BaseBackend):
# The model that contains the configuration required for the paginator PAGINATION_MODEL = { # key = name of the method in the backend "list_resources": { # # name of the kwarg that contains the next token, which should be passed to the backend # backend.list_resources(next_token=..) "input_token": "next_token", # # name of the kwarg that contains the max number of results, which should be passed to the backend "limit_key": "max_results", # # The default limit of the above parameter is not provided "limit_default": 100, # # One or more attributes that guarantee uniqueness for a given resource. # For most resources it will just be an ID, or ARN, which is always unique. # An encoded version of these attributes is used as the NextToken. "unique_attribute": "arn", # Provide a list if only a combination of attributes is guaranteed to be unique "unique_attribute": ["start_date", "execution_arn"], # # By default, an exception will be thrown if the user-provided next_token is invalid "fail_on_invalid_token": True # Default value - no need to specify this # This can be customized to: # - silently fail, and just return an empty list "fail_on_invalid_token": False, # - throw a custom exception, by providing an exception class # The paginator will raise CustomException() or raise CustomException(invalid_token) "fail_on_invalid_token": CustomException }, # another method that will use different configuration options "list_other_things": { ... }, }
# The decorator with the pagination logic @paginate(pagination_model=PAGINATION_MODEL) # Note that this method does not have the 'next_token'/'max_results'-arguments def list_resources(self): # Note that we simply return all resources - the decorator takes care of all pagination magic return self.full_list_of_resources
@paginate(pagination_model=PAGINATION_MODEL) # If we do need the 'next_token'/'max_results'-arguments, just add them to the function # The decorator will only pass them along if required def list_other_things(self, max_results=None): if max_results == "42": # Custom validation magic pass return self.full_list_of_resources