The horizon.utils.memoized Module

exception horizon.utils.memoized.UnhashableKeyWarning

Bases: exceptions.RuntimeWarning

Raised when trying to memoize a function with an unhashable argument.

horizon.utils.memoized.memoized(func)

Decorator that caches function calls.

Caches the decorated function’s return value the first time it is called with the given arguments. If called later with the same arguments, the cached value is returned instead of calling the decorated function again.

The cache uses weak references to the passed arguments, so it doesn’t keep them alive in memory forever.

horizon.utils.memoized.memoized_method(func)

Decorator that caches function calls.

Caches the decorated function’s return value the first time it is called with the given arguments. If called later with the same arguments, the cached value is returned instead of calling the decorated function again.

The cache uses weak references to the passed arguments, so it doesn’t keep them alive in memory forever.

horizon.utils.memoized.memoized_with_request(request_func, request_index=0)

Decorator for caching functions which receive a request argument

memoized functions with a request argument are memoized only during the rendering of a single view because the request argument is a new request instance on each view.

If you want a function to be memoized for multiple views use this decorator.

It replaces the request argument in the call to the decorated function with the result of calling request_func on that request object.

request_function is a function which will receive the request argument.

request_index indicates which argument of the decorated function is the request object to pass into request_func, which will also be replaced by the result of request_func being called.

your memoized function will instead receive request_func(request) passed as argument at the request_index.

The intent of that function is to extract the information needed from the request, and thus the memoizing will operate just on that part of the request that is relevant to the function being memoized.

short example:

@memoized def _get_api_client(username, token_id, project_id, auth_url)

return api_client.Client(username, token_id, project_id, auth_url)

def get_api_client(request):

return _api_client(request.user.username,

request.user.token.id, request.user.tenant_id)

@memoized_with_request(get_api_client) def some_api_function(api_client, *args, **kwargs):

# is like returning get_api_client( # request).some_method(*args, **kwargs) # but with memoization. return api_client.some_method(*args, **kwargs)

@memoized_with_request(get_api_client, 1) def some_other_funt(param, api_client, other_param):

# The decorated function will be called this way: # some_other_funt(param, request, other_param) # but will be called behind the scenes this way: # some_other_funt(param, get_api_client(request), other_param) return api_client.some_method(param, other_param)

See openstack_dashboard.api.nova for a complete example.