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Keep the placeholder structure private to lazyimportobject.c. Move the resolution and attribute lookup code there so it can use the structure without exposing its fields to the eval loop or import code.
Let importlib handle module locks instead of holding the global import lock while resolving a placeholder. Keep active placeholders in a set on the thread and remove them on every exit, including allocation failures. Use the same cycle and recursion checks when a hook returns a placeholder. Keep the source references alive until all attribute lookups finish.
Keep an existing cause or context when resolution fails. Add the import location as a note in that case, without adding the same note twice. Errors without an existing chain still get the declaration as their cause.
Only reuse a concrete attribute from a module that has finished loading. Leave lazy attributes for resolution so module hooks still get a chance. Check the module again after reading its spec, and keep interrupts visible.
Normalize the fromlist before calling the filter and check its items before registering imports. Use one cleanup path and the existing filter accessor. Pass the same five arguments to custom lazy hooks as to __import__.
Resolve lazy __getattr__ and __dir__ hooks before calling them. Treat a hook already being resolved as unavailable so it can import a sibling. Bind a loaded child before removing its pending entry. Recheck the module dict when another thread may have completed the load. Reuse modules already in sys.modules during package cycles, and simplify child registration.
Remember the namespace where lookup found the placeholder and use one helper to resolve and replace it. Only replace a binding that still holds the same placeholder, preserving assignments and deletions during import. Check and replace ordinary dict entries atomically. Keep the mapping protocol for custom namespaces and allow reads from readonly namespaces. Reuse the global lookup helper in the eval loop and remove the duplicate.
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September 27, 2026 14:21
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@brittanyrey this cleans up a bit of the lazy import code by sharing the resolve and replace logic and keeping the placeholder details in one file. It also removes the global import lock around resolution to avoid deadlocks. I split this into 8 commits to make it easier to review. Could you take a look? |
Loading a child can replace the parent binding with the module before we fetch the imported attribute. Keep the module returned by the normal importer so the shared helper can replace it in its actual parent namespace. Other values and deletions still prevent replacement, and custom hooks keep control of their assignments.
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The current implementation has some problems. The eval loop and module attribute lookup repeat the code that resolves a lazy import and replaces its placeholder. These copies behave differently. We also hold the global import lock during resolution, which can deadlock with another thread importing a package.
This moves the placeholder structure and resolution code into
lazyimportobject.c. One helper now resolves the import and updates the namespace where we found the name. It only replaces the value if it is still the same placeholder or the child module that the normal importer just put there. Assignments and deletions made during the import are preserved. For ordinary dicts, the check and replacement are atomic.We also remove the global import lock around resolution. Importlib still locks modules while loading them. Each thread keeps a set of placeholders being resolved to detect cycles. Custom import hooks can now run concurrently.
This removes duplicate lookup and cleanup code. The eval loop and module attribute lookup use the same helper, so they no longer need separate implementations of these rules.
With this design, a placeholder records the module to import and where the import was declared. A name taken from that import holds a reference to the original placeholder and records the attribute to look up. When the name is first used, the resolver follows those references, imports the module and performs the attribute lookups in order. The shared helper then replaces the placeholder in the namespace where it was found, provided that binding still holds the placeholder or that child module.