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ScopeNotInitializedError

Symptom

resolve() or resolve_provider() raises it when a provider's scope is deeper than the container that has to build it. Resolving a REQUEST-scoped provider from the APP container prints:

modern_di.exceptions.container.ScopeNotInitializedError: Cannot resolve dependency chain:
  REQUEST  Session (myapp.providers:7)
  caused by: Provider of scope REQUEST cannot be resolved in container of scope APP.
See: https://modern-di.modern-python.org/troubleshooting/scope-not-initialized-error/

When a shallower provider depends on the deeper one, the chain starts at the shallower provider:

modern_di.exceptions.container.ScopeNotInitializedError: Cannot resolve dependency chain:
  APP      UserCache (myapp.providers:10)
  REQUEST  └─> Session (myapp.providers:7)
  caused by: Provider of scope REQUEST cannot be resolved in container of scope APP.
See: https://modern-di.modern-python.org/troubleshooting/scope-not-initialized-error/

Each chain line names a provider's scope and type and, when it can be found, the module:line where its creator is defined (the class or function, not the Factory(...) line). .provider_scope and .container_scope hold the two scopes in the caused by line.

Cause

The container that has to build the provider is shallower than the provider's scope, in one of two ways:

  • You resolved a provider from a container shallower than the provider's scope, and no container at that scope exists below it yet. The first sample is container.resolve(Session) on the APP container, with no REQUEST child built.
  • A provider depends on a deeper-scoped one, a captive dependency. An APP-scoped UserCache is built in the APP container even when you call resolve(UserCache) on a REQUEST child, and the APP container cannot build the REQUEST-scoped Session it needs. That is why the second sample names container scope APP although the call went to a REQUEST container.

Fix

In the first case, build the deeper container and resolve from it:

# Broken: no REQUEST container exists yet
app_container.resolve(Session)

# Works
request_container = app_container.build_child_container(scope=Scope.REQUEST)
request_container.resolve(Session)

In the captive case a deeper container does not help. Move the depending provider to the deeper scope, or give the dependency a shallower scope if its lifetime allows. container.validate() finds every captive dependency at startup and reports it as InvalidScopeDependencyError, whose page shows both fixes.

See also