[New-bugs-announce] [issue40349] Python3.9 changes col_offset for some ast nodes

[Shantanu]

New submission from Shantanu <hauntsaninja at gmail.com>:

With Python 3.8:
```
Python 3.8.1 (default, Jan 23 2020, 23:36:06) 
[Clang 11.0.0 (clang-1100.0.33.17)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import ast
>>> ast.parse("(a).x").body[0].value.col_offset
1
```

With Python 3.9:
```
Python 3.9.0a5+ (heads/master:799d7d6, Apr  6 2020, 16:05:37) 
[Clang 11.0.0 (clang-1100.0.33.17)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import ast
>>> ast.parse("(a).x").body[0].value.col_offset
0
```

Maybe related to the new parser? I couldn't find what the environment variable to turn it off was.

For context, I'm trying to get mypy tests to pass with 3.9, but the tests make use of specific col_offsets for error reporting. It would be nice if these continued to match with 3.9

----------
messages: 366909
nosy: hauntsaninja
priority: normal
severity: normal
status: open
title: Python3.9 changes col_offset for some ast nodes

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40349>
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