As per this discussion: PEP 703: Making the Global Interpreter Lock Optional (3.12 updates) - #14 by bluetech
As per What is "Pure Python?" - Stack Overflow, which to me is commonly what is understood as “pure Python”, I mean:
mean it’s all implemented in Python, and not (as is sometimes done) with parts written in C or other languages
So no, for this definition of pure Python, I would exclude numpy, or any third party package that requires a compiler, or any call to another process, to install their source distribution.