[docs] [issue25294] Absolute imports fail in some cases where relative imports would work

[Brett Cannon]

Brett Cannon added the comment:

You have to realize, Patrick, that the ability for `from ... import ...` to work in some situations that `import ...` won't is an age-old problem -- they are different at the bytecode level as well as how __import__ handles them -- and starting in Python 3.5 it got tweaked to potentially make the differences more pronounced by making a certain situation involving circular imports not trip users up as much where it was technically feasible to make the change without backwards-compatibility issues. It was a "practicality over purity" decision.

You also said that "PEP 8 prescribes a way of doing something that often won't work" which I disagree with. I think you're reading "absolute import" as synonymous with `import ...` which is not what the term means. In actuality, absolute imports means no leading dot in the name, e.g. `from .x import y` is a relative import while `from z.x import y` is an absolute one (as is `import z.x.y`). If you are using the term "absolute import" in the correct way then I still don't see how PEP 8 is suggesting any practice "that won't often work".

Circular imports are just plain hard to deal with. Due to the long-standing design of import being nothing more than syntactic sugar around exec() we don't get to know statically that a circular import is going to happen, so we can't error out early to tell the user that they *may* be in trouble. And not everyone gets themselves in a position where a circular import dependencies is a problem since it only causes issues when module-level code depends on each other in a circular way (which does include import statements which is where people typically trip themselves up when they get in this situation). I realize you're trying to do the right thing here and get the docs clarified to help newcomers out, but please realize it's just a difficult subject to explain succinctly, especially since a vast majority of people don't get themselves into a position where they have to deal with a circular import.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue25294>
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