You're looking at StableBuild's Deleted PyPI mirror - where we index all deleted packages from the Python package registry.

cvtk
0.3.5b1

This version was deleted from PyPI around 2024-03-23. Installing fails with:
$ pip3 install cvtk==0.3.5b1 ERROR: Could not find a version that satisfies the requirement cvtk==0.3.5b1
View other deleted versions of cvtk

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/2024-03-22/ \ cvtk==0.3.5b1
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Or, download files manually

And install manually via pip:
cvtk-0.3.5b1-py3-none-any.whl (45.0KB)
cvtk-0.3.5b1.tar.gz (29.3KB)