implement from __future__ import annotations
#6117
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tannewt
previously requested changes
Mar 5, 2022
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Is fine by me, once the CI is content. |
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@jepler ready to re-review, thanks. |
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Consider backporting to 7.2.x. |
dhalbert
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Mar 11, 2022
Backport from __future__ import annotations from #6117
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For type annotation purposes, we would like to write code that uses:
This
from __future__is part of PEP 563, which allows postponed evaluation of annotations, so that forward references work without stringifying the annotations. It is available in CPython 3.7 and up, and a lot of CPython .py code uses it. We would like to use it in code that can be used in both CPython and CircuitPython.MicroPython (and CircuitPython) already effectively implement PEP 563 in a no-op way by totally ignoring all annotations. However, MicroPython does not provide a
from __future__ import ...at all. This PR implements a no-op__future__module with a single memberannotations. In CPython, members of__future__are_Featureobjects, with version information. In this PR,annotationsis justTrue.This adds 100 bytes to the Trinket M0 build and presumably other builds. I think this is worth it to allow compatible code.
Note that we cannot do this workaround:
because in CPython, a
from __future__must be absolutely the first statement in a source file. We don't check this restriction, and I don't think it's necessary.