You're looking at StableBuild's Deleted PyPI mirror - where we index all deleted packages from the Python package registry.
sympy-dev was reported malicious
OSV:MAL-2026-450 - Malicious code in sympy-dev (PyPI)

sympy-dev
1.2.4

This version was deleted from PyPI around 2026-01-23. Installing fails with:
$ pip3 install sympy-dev==1.2.4 ERROR: Could not find a version that satisfies the requirement sympy-dev==1.2.4
View other deleted versions of sympy-dev

Install through StableBuild

You can install this package from StableBuild's PyPI snapshots from before the version was deleted:
pip3 install \ -i https://YOUR_API_KEY.pypimirror.stablebuild.com/2026-01-22/ \ sympy-dev==1.2.4
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Or, download files manually

And install manually via pip:
sympy_dev-1.2.4-py3-none-any.whl (6.2MB)
sympy_dev-1.2.4.tar.gz (7.7MB)