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Helpers related to (dynamic) resource retrieval.
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Create a retriever which caches its return values from a simpler callable.
Takes a function which returns things like serialized JSON (strings) and
returns something suitable for passing to `Registry` as a retrieve
function.
This decorator both reduces a small bit of boilerplate for a common case
(deserializing JSON from strings and creating `Resource` objects from the
result) as well as makes the probable need for caching a bit easier.
Retrievers which otherwise do expensive operations (like hitting the
network) might otherwise be called repeatedly.
Examples
--------
.. testcode::
from referencing import Registry
from referencing.typing import URI
import referencing.retrieval
@referencing.retrieval.to_cached_resource()
def retrieve(uri: URI):
print(f"Retrieved {uri}")
# Normally, go get some expensive JSON from the network, a file ...
return '''
{
"$schema": "https://json-schema.org/draft/2020-12/schema",
"foo": "bar"
}
'''
one = Registry(retrieve=retrieve).get_or_retrieve("urn:example:foo")
print(one.value.contents["foo"])
# Retrieving the same URI again reuses the same value (and thus doesn't
# print another retrieval message here)
two = Registry(retrieve=retrieve).get_or_retrieve("urn:example:foo")
print(two.value.contents["foo"])
.. testoutput::
Retrieved urn:example:foo
bar
bar
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