Output closing parenthesis in ast.dump() on separate line

[serhiy-storchaka]

BPO	39989
Nosy	@rhettinger, @terryjreedy, @mdickinson, @ericvsmith, @benjaminp, @serhiy-storchaka, @asottile, @pablogsal
PRs	python/cpython#19039

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields: ```python assignee = None closed_at = None created_at = labels = ['type-feature', 'library', '3.9'] title = 'Output closing parenthesis in ast.dump() on separate line' updated_at = user = 'https://github.com/serhiy-storchaka' ``` bugs.python.org fields: ```python activity = actor = 'Anthony Sottile' assignee = 'none' closed = False closed_date = None closer = None components = ['Library (Lib)'] creation = creator = 'serhiy.storchaka' dependencies = [] files = [] hgrepos = [] issue_num = 39989 keywords = ['patch'] message_count = 6.0 messages = ['364391', '364411', '364426', '364427', '364457', '364824'] nosy_count = 8.0 nosy_names = ['rhettinger', 'terry.reedy', 'mark.dickinson', 'eric.smith', 'benjamin.peterson', 'serhiy.storchaka', 'Anthony Sottile', 'pablogsal'] pr_nums = ['19039'] priority = 'normal' resolution = None stage = 'patch review' status = 'open' superseder = None type = 'enhancement' url = 'https://bugs.python.org/issue39989' versions = ['Python 3.9'] ```

[serhiy-storchaka]

Currently ast.dump() in multiline mode (see bpo-37995) appends closing parenthesis to the end of the line:

>>> import ast
>>> node = ast.parse('spam(eggs, "and cheese")')
>>> print(ast.dump(node, indent=3))
Module(
   body=[
      Expr(
         value=Call(
            func=Name(id='spam', ctx=Load()),
            args=[
               Name(id='eggs', ctx=Load()),
               Constant(value='and cheese')],
            keywords=[]))],
   type_ignores=[])

It uses vertical space more efficiently (which is especially important on Windows console).

But I got a feedback about output closing parenthesis on separate lines (msg363783):

Module(
   body=[
      Expr(
         value=Call(
            func=Name(id='spam', ctx=Load()),
            args=[
               Name(id='eggs', ctx=Load()),
               Constant(value='and cheese')
            ],
            keywords=[]
         )
      )
   ],
   type_ignores=[]
)

It looks more "balanced", but less vertical space efficient. It adds almost 300 lines to 57 examples in Doc/library/ast.rst. And after omitting optional list arguments like keywords=[] and type_ignores=[] (see bpo-39981) the stairs of parenthesis will look even longer.

The proposed PR changes the output of ast.dump() by moving closing parenthesis on separate lines. I am still not sure what output is better.

[mdickinson]

This feels like something that's very much down to personal preference.

I also prefer the closing "]" and ")" characters on their own lines, but I'd be happy with an argument to ast.dump giving me that option.

[ericvsmith]

For what it's worth (which might not be much), here is what black produces:

Module(
    body=[
        Expr(
            value=Call(
                func=Name(id="spam", ctx=Load()),
                args=[Name(id="eggs", ctx=Load()), Constant(value="and cheese")],
                keywords=[],
            )
        )
    ],
    type_ignores=[],
)

I agree with Mark: it's all probably personal preference, and I'd be okay either way.

[mdickinson]

Ah yes; looking at the black output, there's also an opportunity for an exciting discussion about trailing commas here :-)

[terryjreedy]

The current output looks like Python code. The proposed revision looks more like C, and I find the example above less readable with the prominence given to what is close to noise. The difference is part of the reason I left C for Python over 2 decades ago. Please make the alternative an option. The preferred form depends on the person and possibly the AST. (The example in Pablo's message is quite different.)

[341ce0e2-bdbb-4bd4-99e6-746f11201a3f]

fwiw, astpretty's output looks like the black output: https://github.com/asottile/astpretty

>>> astpretty.pprint(ast.parse('if x == y: y += 4').body[0])
If(
    lineno=1,
    col_offset=0,
    test=Compare(
        lineno=1,
        col_offset=3,
        left=Name(lineno=1, col_offset=3, id='x', ctx=Load()),
        ops=[Eq()],
        comparators=[Name(lineno=1, col_offset=8, id='y', ctx=Load())],
    ),
    body=[
        AugAssign(
            lineno=1,
            col_offset=11,
            target=Name(lineno=1, col_offset=11, id='y', ctx=Store()),
            op=Add(),
            value=Num(lineno=1, col_offset=16, n=4),
        ),
    ],
    orelse=[],
)