[New-bugs-announce] [issue39069] Move ast.unparse() function to a different module

[STINNER Victor]

New submission from STINNER Victor <vstinner at python.org>:

Pablo Galingo Salgado recently moved Tools/parser/unparse.py to a ast.unparse() function.

Pablo made a change using functools. The additional "import functools" made "import ast" slower and so Pablo reverted his change:

* https://github.com/python/cpython/pull/17376
* https://bugs.python.org/issue38870

The question of using contextlib comes back in another ast.unparse change to get @contextlib.contextmanager:

* https://github.com/python/cpython/pull/17377#discussion_r350239415

On the same PR, I also proposed to use import enum:

* https://github.com/python/cpython/pull/17377#discussion_r357921289

There are different options to not impact "import ast" performance:

* Move ast.unparse() code into a new module
* Write to code so imports can be done lazily

"from ast import unparse" or "ast.unparse()" can be kept using a private _ast_unparse module and add a __getattr__() function to Lib/ast.py to lazily bind _ast_unparse.unparse() to ast.unparse().

Other options:

* Avoid cool enum and functools modules, and use simpler Python code (that makes me sad, but it's ok)
* Accept to make "import ast" slower
* Remove ast.unparse(): I don't think that anyone wants this, ast.unparse() was approved on python-dev.

----------
components: Library (Lib)
messages: 358496
nosy: pablogsal, vstinner
priority: normal
severity: normal
status: open
title: Move ast.unparse() function to a different module
versions: Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue39069>
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