Fix pip config parsing for multiple extra-index-urls

[harkrish-1]

Summary

• Fix Pip.indices() to correctly parse multiple extra-index-url values from pip config
• When pip config contains multiple extra-index-urls, pip config list outputs them separated by literal \n characters (backslash + n, not actual newlines)
• The previous regex (\s+) only split on whitespace, so multiple URLs were treated as a single mangled value
• The fix adds literal \n as an additional split delimiter: r"\\n|\s+"

Tests

• Unit tests added/updated
• Reproduction script provided (required for Core Runtime)
• CI passes
• If tests are impractical: explain why below and provide manual evidence above

Non-Goals

AI Tool Usage

• No AI tools were used in this contribution
• AI tools were used (describe below)

Used claude code to identify and fix this bug, I completely understand the changes made

[greptile-apps]

Greptile Summary

This PR fixes Pip.indices() to split multiple extra-index-url values that pip config list emits as a single string joined by literal (backslash + n) characters. The one-line regex change and accompanying regression test are both correct and minimal.

Confidence Score: 5/5

Safe to merge; the fix is correct, the test validates the regression, and the only remaining finding is a minor defensive-coding suggestion.

No P0 or P1 issues. The single finding (empty strings from split) is a pre-existing edge case that the PR doesn't worsen in any realistic pip output scenario, and is P2 only.

No files require special attention.

Important Files Changed

Filename	Overview
metaflow/plugins/pypi/pip.py	Adds \n literal as a split delimiter in indices() to correctly parse multiple extra-index-url values from pip config; fix is logically correct but may admit empty strings into the result list in edge cases
test/unit/test_pip_indices.py	New regression test correctly simulates the literal \n separator via a raw string and verifies that both URLs are parsed as distinct entries

_{Reviews (3): Last reviewed commit: "Add unit tests for Pip.indices() config ..." | Re-trigger Greptile}

[harkrish-1]

@savingoyal @saikonen please review and add your feedback. Simple one line change, shouldn't need a lot of time to review.

[talsperre]

Please use pytest, magicmock (pytest-mock plugin), and monkeypatch for the tests. Within pytest, we prefer to use fixtures and non-class-based tests.

[talsperre]

Also make sure to setup the pre-commit hooks insce your code fails on the pre-commit checks in GitHub actions.

[talsperre]

Also the appropriate location for this test file should be inside test/plugins/pip (https://github.com/Netflix/metaflow/tree/master/test/plugins) - i.e., create a new directory for pip and add this test in there.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

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[saikonen]

Change looks straightforward, good catch with this one.

Can you address the other pending review comments still? Otherwise this is good to go.