fix: resolve normalized package names to their module

[mscolnick]

Closes #9801

Problem

PackageManager.package_to_module was case-sensitive. PyPI package names,
however, are case-insensitive and treat runs of -, _, and . as
equivalent (PEP 503). uv normalizes names when it writes them into a
notebook's PEP 723 script metadata — e.g. Pillow becomes pillow — so the
reverse lookup silently failed:

mgr.package_to_module("pillow")        # -> "pillow"        (should be "PIL")
mgr.package_to_module("Scikit-Learn")  # -> "Scikit_Learn"  (should be "sklearn")

In a sandbox this is the root cause of the confusing PIL/Pillow behavior in
the issue: after marimo installs pillow, it maps the installed package name
back to a module to decide which cells to re-run. Because pillow resolved to
the module pillow (which nothing imports) instead of PIL, the cell that
imports PIL was never re-run, forcing the user to manually toggle the import
every time they reopened the notebook.

Fix

package_to_module now falls back to a PEP 503-normalized lookup when there's
no exact match, before guessing. The known-name mapping is still consulted
exactly first, so existing casing is preserved.

mgr.package_to_module("pillow")        # -> "PIL"
mgr.package_to_module("PILLOW")        # -> "PIL"
mgr.package_to_module("Scikit-Learn")  # -> "sklearn"
mgr.package_to_module("scikit_learn")  # -> "sklearn"

Unknown packages still fall back to the previous - → _ behavior.

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Jul 13, 2026 6:45pm

[Copilot]

Pull request overview

This PR fixes PackageManager.package_to_module reverse lookups when package names are PEP 503-normalized (case-insensitive and treating runs of -, _, . as equivalent), which is important for environments where uv writes normalized dependency names into PEP 723 metadata (e.g. Pillow → pillow). This addresses the “PIL/Pillow” sandbox rerun behavior described in #9801 by correctly mapping normalized package names back to their canonical import module (e.g. pillow → PIL).

Changes:

• Add a PEP 503 normalization helper and a lazily-built normalized reverse mapping for package-name-to-module lookups.
• Update package_to_module to try: exact match → normalized match → legacy -→_ heuristic.
• Add a regression test covering normalized/case-variant inputs for Pillow/PIL and scikit-learn/sklearn.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
marimo/_runtime/packages/package_manager.py	Adds PEP 503 normalization and a normalized fallback lookup in package_to_module while preserving exact-match behavior first.
tests/_runtime/packages/test_pypi_package_manager.py	Adds regression test ensuring normalized/case-variant package names resolve to the correct module.

[cubic-dev-ai]

No issues found across 2 files

Architecture diagram

sequenceDiagram
    participant Caller as Cell / Kernel
    participant PM as PackageManager
    participant Init as _initializeMappings()
    participant ExactMap as _repo_name_to_module_name
    participant NormMap as _normalized_repo_name_to_module_name
    participant Normalize as _normalize_package_name()

    Note over Caller,Normalize: After uv installs a package, marimo resolves its name<br/>to module to decide which cells to re-run (PR issue #9801)

    Caller->>PM: package_to_module("pillow")
    activate PM

    PM->>Init: _initialize_mappings() if None
    activate Init
    Init->>ExactMap: reverse of module_name_to_repo_name
    Init->>NormMap: normalize keys of ExactMap (NEW)
    deactivate Init

    PM->>ExactMap: "pillow" exact match?
    ExactMap-->>PM: miss (only has "Pillow")

    alt Exact match miss
        PM->>Normalize: _normalize_package_name("pillow")
        activate Normalize
        Normalize-->>PM: "pillow"
        deactivate Normalize

        PM->>NormMap: "pillow" normalized key exists?
        NormMap-->>PM: yes → "PIL"
        Note over PM: NEW: PEP 503 normalized lookup<br/>preserves correct module name

        PM-->>Caller: "PIL"
    else Exact match found (e.g., "Pillow")
        ExactMap-->>PM: "PIL"
        PM-->>Caller: "PIL"
    end

    deactivate PM

    Note over Caller,Normalize: Unknown packages still fall back to original `-` → `_` guess

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[github-actions]

🚀 Development release published. You may be able to view the changes at https://marimo.app?v=0.23.15-dev19