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 correctly split multiple extra-index-url values from pip config list output, where pip serializes multi-value entries as a single string with literal (backslash + n) separators rather than actual newlines. A targeted regex change and a corresponding regression test are the only modifications.

• pip.py: regex updated from \\s+ to r\"\\\ |\\s+\" so literal \ separators are recognized as delimiters alongside whitespace.
• test_pip_indices.py: new pytest file that mocks _call and asserts both URLs are parsed out correctly from a realistic multi-URL config string.

Confidence Score: 5/5

Safe to merge — the change is a narrow, well-tested regex fix with no impact on other code paths.

The fix is minimal and clearly correct: it adds \ as an additional split delimiter so that pip's literal-backslash-n separator between multiple index URLs is handled properly. The regression test exercises the exact scenario. No existing behavior is altered for the single-URL case.

No files require special attention.

Important Files Changed

Filename	Overview
metaflow/plugins/pypi/pip.py	Adds \\n as a split delimiter in indices() so multiple extra-index-url values emitted by pip config list as literal backslash-n are parsed correctly.
test/plugins/pip/test_pip_indices.py	New regression test that mocks _call and verifies multi-URL parsing with literal \n separators; covers the happy path introduced by the fix.
test/plugins/pip/init.py	Empty init file to make the new test directory a proper Python package.

_{Reviews (9): Last reviewed commit: "Merge branch 'master' into fix/pip-confi..." | 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]

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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[harkrish-1]

@talsperre @saikonen addressed all comments!

[harkrish-1]

@talsperre @saikonen Please review this