I Don't Like NumPy
Published on: 2025-07-07 14:05:22
They say you can’t truly hate someone unless you loved them first. I don’t know if that’s true as a general principle, but it certainly describes my relationship with NumPy.
NumPy, by the way, is some software that does computations on arrays in Python. It’s insanely popular and has had a huge influence on all the popular machine learning libraries like PyTorch. These libraries share most of the same issues I discuss below, but I’ll stick to NumPy for concreteness.
NumPy makes easy things easy. Say A is a 5×5 matrix, x is a length-5 vector, and you want to find the vector y such that Ay=x . In NumPy, that would be:
y = np . linalg . solve ( A , x )
So elegant! So clear!
But say the situation is even a little more complicated. Say A is a stack of 100 5×5 matrices, given as a 100×5×5 array. And say x is a stack of 100 length-5 vectors, given as a 100×5 array. And say you want to solve Aᵢyᵢ=xᵢ for 1≤i≤100 .
If you could use loops, this would be easy:
y = np . empty_like ( x ) for i
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