Everyone uses pure python for purely computational tasks. numpy or pytorch has far too few operation to even count as all the computational task. e.g. most of the operations of pandas is written in pure python, and at times I found using specialised libraries could give 10x improvement but with blow to developer experience compared to python.
No one said they don't. Just there still are and always will be parts which are computationally heavy but written in python. e.g. pandas map is 300x slower than numpy map[1] for the same operation. But not everything could be vectorized and even if some complex function could be vectorized it will involve multiple passes over memory for the same array.
Every time you use a for loop, addition or multiplication operators, array indexing, assingment to numerical variable in Python, you are using exactly what is benchmarked in matmul.
