Hi, all. There is design discussion which is deferred blocker of 3.7. https://bugs.python.org/issue32911 ## Background An year ago, I moved docstring in AST from statements list to field of module, class and functions. https://bugs.python.org/issue29463 Without this change, AST-level constant folding was complicated because "foo" can be docstring but "fo" + "o" can't be docstring. This simplified some other edge cases. For example, future import must be on top of the module, but docstring can be before it. Docstring is very special than other expressions/statement. Of course, this change was backward incompatible. Tools reading/writing docstring via AST will be broken by this change. For example, it broke PyFlakes, and PyFlakes solved it already. https://github.com/PyCQA/pyflakes/pull/273 Since AST doesn't guarantee backward compatibility, we can change AST if it's reasonable. Last week, Mark Shannon reported issue about this backward incompatibility. As he said, this change losted lineno and column of docstring from AST. https://bugs.python.org/issue32911#msg312567 ## Design discussion And as he said, there are three options: https://bugs.python.org/issue32911#msg312625
It seems to be that there are three reasonable choices: 1. Revert to 3.6 behaviour, with the addition of `docstring` attribute. 2. Change the docstring attribute to an AST node, possibly by modifying the grammar. 3. Do nothing.
1 is backward compatible about reading docstring.
But when writing, it's not DRY or SSOT. There are two source of docstring.
For example: `ast.Module([ast.Str("spam")], docstring="egg")`
2 is considerable. I tried to implement this idea by adding `DocString`
statement AST.
https://github.com/python/cpython/pull/5927/files
While it seems large change, most changes are reverting the AST changes.
So it's more closer to 3.6 codebase. (especially, test_ast is very
close to 3.6)
In this PR, `ast.Module([ast.Str("spam")])` doesn't have docstring for
simplicity. So it's backward incompatible for both of reading and
writing docstring too.
But it keeps lineno and column of docstring in AST.
3 is most conservative because 3.7b2 was cut now and there are some tools
supporting 3.7 already.
I prefer 2 or 3. If we took 3, I don't want to do 2 in 3.8. One
backward incompatible
change is better than two.
Any thoughts?
--
INADA Naoki