Run sage notebook without sage.all imported

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But my point is that I don't want to use from sage.all import *. I only need a couple libraries. If I try to import a sage library from a Python 2 kernel, I either get an ImportError or the kernel crashes. Is it really only possible to import the entire sage library or nothing at all?

Short answer: no

Longer answer: it is complicated to make work together many libraries and the fact that Python is easily subject to cyclic imports. The initialization of the Sage module (in sage.all) is quite possibly not optimal as it does initialize and import everything. I agree with you that the initialization of the libraries should be made more local but it is currently not the case.

Advertisement: SageMath is a collaborative open source project. You are very welcome to propose concrete improvement by submitting code to the trac server.

I'm quite certain it's possible to speed of Sage initialization by importing just a smaller set of core modules, and I would like to be able to do that too. Even with the import cycles (some of which I believe can be broken with appropriate refactoring, although some others are unavoidable), I think it should be possible to get imports from sage working without importing as much as sage.all does. It's something I've always wanted to work on but it is a daunting task no doubt.

That makes sense, thanks for clearing that up.