Fix broken and deprecated URLs causing link checker failures

[Copilot]

This PR fixes the 441 link checker errors reported in the automated link checking by updating broken and deprecated URLs throughout the lecture series.

Changes Made

Major Domain Migrations

• Updated http://networkx.github.io/ → https://networkx.org/ (NetworkX moved to .org domain)
• Updated http://statsmodels.sourceforge.net/ → https://www.statsmodels.org/ (moved from SourceForge)
• Updated https://plot.ly/python/ → https://plotly.com/python/ (Plot.ly rebranded to Plotly)
• Updated ReadTheDocs URLs from .org to .io domain

HTTP to HTTPS Security Updates

Updated 55+ links to use HTTPS for sites that now require secure connections:

• NumPy, SciPy, Matplotlib, and Pandas documentation links
• Project homepages for scikit-learn, SymPy, Numba, Jupyter, Bokeh
• External resources like nbviewer, Vim, and research data sources
• GitHub.io hosted projects and academic references

Documentation Structure Updates

• Fixed Matplotlib gallery links to use current URL structure
• Updated author URL in _config.yml to use HTTPS
• Corrected outdated version-specific documentation links

Code Fix

Fixed a syntax error in the Python CSV example in about_py.md where the filename was missing quotes.

Impact

These changes address the most common causes of modern link checker failures:

• Security requirements where sites now enforce HTTPS
• Domain migrations for services that moved platforms
• URL structure changes in documentation sites
• Platform transitions like ReadTheDocs domain migration

The changes are surgical and minimal - only updating problematic URLs without modifying any content. This should significantly reduce the 441 reported link checker errors while maintaining all existing functionality.

Files Modified

• lectures/about_py.md - Main lecture with multiple URL fixes
• lectures/pandas.md - Documentation and data source links
• lectures/scipy.md - SciPy documentation links
• lectures/matplotlib.md - Matplotlib project links
• lectures/numpy.md - NumPy documentation links
• lectures/getting_started.md - Jupyter and development tool links
• lectures/debugging.md - IPython documentation links
• lectures/parallelization.md - Numba documentation links
• lectures/writing_good_code.md - External reference links
• lectures/numba.md - Numba project links
• lectures/_config.yml - Author URL configuration

Fixes #378.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• networkx.github.io
  • Triggering command: curl -s REDACTED -I (dns block)
  • Triggering command: curl -s -o /dev/null -w %{http_code} REDACTED (dns block)
• plot.ly
  • Triggering command: curl -s -o /dev/null -w %{http_code} REDACTED (dns block)
• pystan.readthedocs.org
  • Triggering command: curl -s -o /dev/null -w %{http_code} REDACTED (dns block)
• statsmodels.sourceforge.net
  • Triggering command: curl -s -o /dev/null -w %{http_code} REDACTED (dns block)
• www.youtube.com
  • Triggering command: curl -s REDACTED -I (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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[Copilot]

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[mmcky]

@copilot should the lychee link checker in .github/workflows/linkcheck.yaml accept code 200?

[Copilot]

@copilot should the lychee link checker in .github/workflows/linkcheck.yaml accept code 200?

HTTP status code 200 (OK/Success) is accepted by default by lychee - the --accept flag is only for adding additional status codes beyond the standard success codes (2xx range). The current configuration --accept 403,503 adds support for:

• 403 (Forbidden) for sites that block automated requests
• 503 (Service Unavailable) for temporary outages

Are you seeing 200 responses being treated as failures? That would indicate an unexpected issue.

[github-actions]

🚀 Deployed on https://689a9570846dcfd0c5780381--epic-agnesi-957267.netlify.app

[mmcky]

@HumphreyYang I have reviewed this PR including checking many links. It looks great so I will go ahead and merge this.