PEP 690: Lazy Imports Again

PEPs
10

One piece of personal feedback is I think there’s now too many ways to control whether lazy loading is on/off:

  1. -L
  2. importlib.set_lazy_imports()
  3. importlib.enable_lazy_imports_in_module()
  4. Import in a try
  5. Import on a with

Do we need so my knobs? For instance, you can do option 3 by inverting the logic and using option 5 with a do-nothing context manager, e.g.:

with force_eager_importing():
   ...

Since that function only has module-level effects, that suggests you already have control over the code in that module. As such, you can choose how to handle that situation however you want.

For turning lazy importing on later, since you can control what’s eager I’m assuming this is for indirect imports that have side-effects (e.g. A → B w/ side-effects)? But you could forcibly do that by importing B before you import A, and do both eagerly in a try/with. I see this potentially falling apart if you can’t import B before A because of some side-effect requirement on A. But in that case, you could still import A and then B in the same eager block for the same effect.

Personally, the way I would suggest doing this is:

  1. Emit IMPORT bytecode for anything at the module scope not in a block that can be eager or lazy based on a flag in sys (or just within try)
  2. Emit an EAGER_IMPORT bytecode for everything else
  3. Have importlib be called differently based on which bytecode is used so it knows which module object to construct (by default, otherwise I haven’t looked at how your proposed functions communicate with the deep innards of importlib)
  4. If you want people to control what things do, then let the flag in sys be writable

After that, it’s up to people to come up with their own APIs to control lazy/eager importing by flipping stuff around in sys (e.g. their own context managers since people should not be doing imports in threads to begin with). Otherwise I’m afraid you’re going to be constantly chasing everyone’s desires of that one API they want for their thinking of how this should work and it will vary as much as how people do imports (which is a lot).

5 Likes