[mikegit123git]

Summary

Fixes #850.

Application.load_config_file() currently strips the extension from the specified filename and loads both .py and .json configuration files sharing the same basename.

This is unexpected when an explicit filename is provided and may cause unintended Python code execution when loading a JSON configuration.

This PR:

• Respects explicitly specified .py and .json extensions, loading only the requested file type.
• Preserves the existing behavior for filenames without an extension, including JSON precedence.
• Preserves configuration search-path priority and error handling.
• Adds 12 regression tests covering file selection, path handling, error cases, and backward compatibility.
• Updates the configuration documentation.

Reproduction

Given:

foo.py

c.Foo.bar = 10

foo.json

{"Foo": {"bar": 11}}

Calling app.load_config_file(py_path) previously produced bar == 11 because both files were loaded.

After the fix, bar == 10 and only foo.py is loaded.

Testing

Validated locally on Ubuntu 22.04 with Python 3.10:

• Full pytest suite: 722 passed, 1 skipped
• Ruff lint checks: passed
• Ruff formatting checks: passed
• mypy: passed (24 source files)
• Git diff whitespace checks: passed

The local documentation build was blocked during dependency installation. GitHub CI verification is pending.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.35%. Comparing base (a576f24) to head (f060e6f).

Components	Coverage Δ
traitlets	85.82% <100.00%> (+0.18%)	⬆️
tests	99.09% <100.00%> (+0.01%)	⬆️

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