With Python 3.5 and 3.6 list comprehensions, generators and tuples have the col_offset for their ast nodes off by 1:```import astast.parse('{a for a in range(3)}').body[0].value.col_offset>> 0  # set comprehension correctast.parse('{a: 1 for a in range(3)}').body[0].value.col_offset>> 0  # dict comprehension correctast.parse('[a for a in range(3)]').body[0].value.col_offset>> 1  # list comprehension wrong!ast.parse('(a for a in range(3))').body[0].value.col_offset>> 1  # generator comprehension wrong!ast.parse('[1, 2, 3]').body[0].value.col_offset>> 0  # list correctast.parse('{1, 2, 3}').body[0].value.col_offset>> 0  # set correctast.parse('{1: 1, 2: 2, 3: 3}').body[0].value.col_offset>> 0  # dict correctast.parse('(1, 2, 3)').body[0].value.col_offset>> 1  # tuple wrong!```I haven't tried 3.4, the issue could be there too.There are some other related issues#16806 and#21295 but they don't seem quite the same.

For list comprehensions and generator expressions this is definitely a bug. But tuples syntax technically does not include surrounded parentheses.There is also a problem with generator expression passes as a single argument. Generator expression parentheses can be collapsed with function call parentheses: f(a for a in b).PR 10633 makes the following changes:* Fixes position for list comprehensions and generator expressions.* If generator expression parentheses are be collapsed with function call parentheses, the position of the AST node for the generator expression points to the left parenthesis.* For tuples surrounded with parentheses, the position of the AST node points to the left brace. For tuples without parentheses, it points to the position of the first tuple item.I am not sure whether these changes should be backported to maintained versions.

I am not sure what parts of this PR should be backported if either.

Yeah, it's a tough call because it's one of those things others have probably worked around already, so backporting would break the work-arounds.If you don't want to bother backporting, Serhiy, I think it would be fine to not do it.

New changesetb619b097923155a7034c05c4018bf06af9f994d0 by Serhiy Storchaka in branch 'master':bpo-31241: Fix AST node position for list and generator comprehensions. (GH-10633)https://github.com/python/cpython/commit/b619b097923155a7034c05c4018bf06af9f994d0