fix(pythonic-resources): ResourceDependency with default causes RecursionError

[gambletan]

Summary

Fixes #33650.

When a ConfigurableResource subclass instance is used as a class-level default for a ResourceDependency field, accessing that field triggered infinite recursion:

class Outer(ConfigurableResource):
    inner: ResourceDependency[Inner] = Inner()  # Inner() is a data descriptor

    def greet(self):
        return self.inner.val  # RecursionError

Root cause: ConfigurableResourceFactory inherits __get__/__set__ from TypecheckAllowPartialResourceInitParams, making every ConfigurableResource instance a Python data descriptor. When Inner() is stored as a class attribute of Outer, accessing outer.inner called TypecheckAllowPartialResourceInitParams.__get__ which called getattr(obj, self._assigned_name), which re-triggered __get__ — infinite recursion.

A secondary effect was that Pydantic could not read the Inner() class-level default (because Inner().__get__(None, Outer) raised AttributeError before the fix), causing _nested_resources to be empty and the nested resource's lifecycle to be skipped.

Fix — two changes:

1. TypecheckAllowPartialResourceInitParams.__get__/__set__ (typing_utils.py):

   • __get__: return self when obj is None (class-level access) so Pydantic can read the default. When obj is an instance, read from obj.__dict__ directly to bypass the descriptor protocol.
   • __set__: use object.__setattr__ instead of setattr to avoid re-entering the descriptor.

2. ConfigurableResourceFactory.__init__ (resource.py):
   After super().__init__(), Pydantic has populated self.__dict__ with all values including defaults. Re-run separate_resource_params over self.__dict__ to pick up resource-typed fields populated from defaults, ensuring they are tracked in _nested_resources and resolved at execution time.

Test plan

• New regression test test_resource_dependency_with_default_no_recursion covers sensor context
• New test test_resource_dependency_with_default_in_asset covers asset execution
• All existing resource tests pass (243 passed including 2 new)
• All pythonic config tests pass (140 passed, 1 skipped)

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

This PR fixes a RecursionError that occurred when a ConfigurableResource subclass instance was used as a class-level default for a ResourceDependency field. The root cause was that every ConfigurableResource instance is a Python data descriptor (via TypecheckAllowPartialResourceInitParams), so storing one as a class attribute caused __get__ → getattr(obj, name) → __get__ → … infinite recursion.

Changes:

• typing_utils.py — __get__ now short-circuits on class-level access (obj is None) by returning self, allowing Pydantic to read the class default. For instance access it reads from obj.__dict__ directly, bypassing the descriptor protocol and eliminating the recursion. __set__ is updated to use object.__setattr__ for the same reason.
• resource.py — After super().__init__() (when Pydantic has populated all defaults), the __init__ of ConfigurableResourceFactory re-scans self.__dict__ with separate_resource_params to pick up any resource-typed fields that were set from class-level defaults. This ensures they are tracked in _nested_resources and resolved at execution time. The merge order ({**all_resource_pointers, **resource_pointers}) correctly lets explicitly provided values override defaults.
• test_nesting.py — Two new regression tests: one covering sensor context, one covering asset execution, verifying both the recursion fix and that explicit overrides continue to work.

Confidence Score: 5/5

• Safe to merge — the fix is targeted, correct, and well-tested with no behaviour changes outside the broken default-descriptor path.
• The root cause is accurately diagnosed and both parts of the fix (descriptor __get__/__set__ and the post-init re-scan) are correct. The merge order in the re-scan preserves explicit overrides. Existing tests all pass alongside two new regression tests covering the exact failure modes. The only findings are a dead-code else branch in __set__, a stray blank line, and a duplicate test pattern — none of which affect correctness or production reliability.
• No files require special attention.

Important Files Changed

Filename	Overview
python_modules/dagster/dagster/_config/pythonic_config/typing_utils.py	Fixed recursive descriptor loop: __get__ now returns self on class-level access and reads from obj.__dict__ to bypass the protocol. __set__ uses object.__setattr__, but contains a dead-code else branch.
python_modules/dagster/dagster/_config/pythonic_config/resource.py	Post-super().__init__() re-scan of self.__dict__ correctly picks up resource-typed fields populated from class-level defaults; merge order {**all_resource_pointers, **resource_pointers} properly preserves explicit overrides. Minor extra blank line.
python_modules/dagster/dagster_tests/core_tests/resource_tests/pythonic_resources/test_nesting.py	Two new regression tests covering sensor context and asset execution paths for the fix; solid coverage of default, explicit-override, and nested-resource-tracking scenarios. Minor redundancy between Pattern 1 and Pattern 4.

Sequence Diagram

sequenceDiagram
    participant User
    participant OuterResource
    participant Pydantic
    participant TypecheckDescriptor as TypecheckAllowPartialResourceInitParams.__get__
    participant InstanceDict as obj.__dict__

    Note over User,InstanceDict: BEFORE fix — RecursionError
    User->>OuterResource: outer.inner
    OuterResource->>TypecheckDescriptor: __get__(obj=outer, owner=Outer)
    TypecheckDescriptor->>TypecheckDescriptor: getattr(outer, "inner")
    TypecheckDescriptor->>TypecheckDescriptor: __get__(obj=outer, owner=Outer)
    TypecheckDescriptor-->>TypecheckDescriptor: ∞ RecursionError

    Note over User,InstanceDict: AFTER fix — correct resolution
    User->>OuterResource: outer.inner
    OuterResource->>TypecheckDescriptor: __get__(obj=outer, owner=Outer)
    TypecheckDescriptor->>InstanceDict: obj.__dict__["inner"]
    InstanceDict-->>TypecheckDescriptor: InnerResource instance
    TypecheckDescriptor-->>User: InnerResource instance

    Note over User,InstanceDict: Class-level access (Pydantic reading default)
    Pydantic->>TypecheckDescriptor: __get__(obj=None, owner=Outer)
    TypecheckDescriptor-->>Pydantic: self (descriptor/default InnerResource instance)

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_{Reviews (1): Last reviewed commit: "fix: ResourceDependency with default no ..." | Re-trigger Greptile}

[greptile-apps]

Dead-code else branch in __set__

Python's descriptor protocol never calls __set__ with obj=None — __set__ is only invoked on instances, not via class-level attribute assignment (which would replace the descriptor in the class __dict__ directly). The else branch therefore can never be reached, and if it somehow were, setattr(None, …) would raise TypeError.

Consider simplifying to just the guard:

Suggested change

	if obj is not None:
	object.__setattr__(obj, self._assigned_name, value)
	else:
	setattr(obj, self._assigned_name, value)
	if obj is not None:
	object.__setattr__(obj, self._assigned_name, value)

[greptile-apps]

Extra blank line between top-level functions

Three blank lines are present between separate_resource_params and _call_resource_fn_with_default; PEP 8 recommends two.

Suggested change

	return out
	return out
	def _call_resource_fn_with_default(

_{Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!}

[greptile-apps]

Duplicate test pattern

"Pattern 4" is identical to "Pattern 1" — both create a build_sensor_context with OuterResource() and assert outer.greet() == "hello". Consider replacing with a distinct scenario (e.g. verifying the sensor body runs via list(my_sensor(ctx))) or removing it to reduce noise.

_{Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!}