Multiple context expressions do not support parentheses for continuation across lines

[Julian]

BPO	12782
Nosy	@gvanrossum, @warsaw, @birkenfeld, @atsuoishimoto, @ncoghlan, @benjaminp, @ezio-melotti, @merwok, @stevendaprano, @bitdancer, @ambv, @Julian, @serhiy-storchaka, @asottile, @pablogsal, @thautwarm, @isidentical, @websurfer5, @jack1142

^{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:

assignee = 'https://github.com/pablogsal'
closed_at = <Date 2020-06-25.19:11:20.497>
created_at = <Date 2011-08-19.02:10:17.157>
labels = ['interpreter-core', 'type-feature', '3.10']
title = 'Multiple context expressions do not support parentheses for continuation across lines'
updated_at = <Date 2022-01-16.22:14:02.746>
user = 'https://github.com/Julian'

bugs.python.org fields:

activity = <Date 2022-01-16.22:14:02.746>
actor = 'eric.araujo'
assignee = 'pablogsal'
closed = True
closed_date = <Date 2020-06-25.19:11:20.497>
closer = 'pablogsal'
components = ['Interpreter Core']
creation = <Date 2011-08-19.02:10:17.157>
creator = 'Julian'
dependencies = []
files = []
hgrepos = []
issue_num = 12782
keywords = ['patch']
message_count = 29.0
messages = ['142411', '142549', '142550', '142631', '142658', '142750', '180512', '180514', '180515', '236083', '236121', '293660', '326637', '326639', '326645', '326648', '326727', '327875', '346137', '346157', '347025', '363755', '372383', '372384', '372385', '372388', '410726', '410728', '410729']
nosy_count = 21.0
nosy_names = ['gvanrossum', 'barry', 'georg.brandl', 'ishimoto', 'ncoghlan', 'benjamin.peterson', 'ezio.melotti', 'eric.araujo', 'steven.daprano', 'r.david.murray', 'lukasz.langa', 'Julian', 'serhiy.storchaka', 'ulope', 'Anthony Sottile', 'pablogsal', 'thautwarm', 'BTaskaya', 'Terry Davis', 'Jeffrey.Kintscher', 'jack1142']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue12782'
versions = ['Python 3.10']

[Julian]

Using multiple with statements across multiple lines does not support using parens to break them up:

with (open("a_really_long_foo") as foo,
      open("a_really_long_bar") as bar):
    pass

Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "demo.py", line 19
    with (open("a_really_long_foo") as foo,
                                    ^
SyntaxError: invalid syntax

Also, without convoluting things, import also does not support doing so, and is the only other example I can think of of a compound statement that forces you to either be redundant or bite your teeth and use \, despite the fact that PEP-328 gave us parens for from imports.

(I did not find a discussion as to why import didn't grow it as well, so please correct me as I'm sure it must have been discussed before).

It's understandably a lot rarer to need multiple lines when importing, but it'd be nice if all compound statements uniformly allowed the same continuation syntax.

[merwok]

I agree it’s unfortunate that we have to use backslashes to have multi-line with statements.

[birkenfeld]

is the only other example I can think of

One similar example would be "raise" in Python 2.

all compound statements uniformly allowed the same continuation syntax.

This is not true: only "import-as" allows this syntax. All other uses of parentheses for continuation are continuations of *expressions*.

[bitdancer]

Following on to Georg's comment about expressions, as a workaround, note
that:

  with (
     open('abc')) as foo:

works.

[ncoghlan]

As Georg noted, only individual expressions get parentheses based continuations automatically. For statement level use of comma separation, it's decided on a case-by-cases basis as to whether we think it is a legitimate usage based on our style guidelines.

That's why 'from location import (name1, name2)' is allowed, but 'import (name1, name2)' is not: we explicitly advise against importing too many modules in a single import statement, but importing multiple names from a single location is often a useful thing to do.

However, while the multiple context expression use case is reasonable, there may be a grammar ambiguity problem in this case, since (unlike from-import) with statements allow arbitrary subexpressions.

[Julian]

we explicitly advise against importing too many modules in a single import statement, but importing multiple names from a single location is often a useful thing to do.

Cool. I imagined this had to do with it.

there may be a grammar ambiguity problem in this case, since (unlike from-import) with statements allow arbitrary subexpressions.

Sorry, can you possibly clarify where the ambiguity might come in?

[atsuoishimoto]

In Python 3.3, we have contextlib.ExitStack() for multiple contexts.
So, perhaps we can close this issue?

[ezio-melotti]

If this can't be fixed I think it should be at least documented in the FAQs.

[serhiy-storchaka]

There is a discussion about this on Python-Ideas:

http://comments.gmane.org/gmane.comp.python.ideas/17597
http://mail.python.org/pipermail/python-ideas/2012-October/017610.html

[stevendaprano]

This has come up on Python-Ideas again:

http://permalink.gmane.org/gmane.comp.python.ideas/32002

https://mail.python.org/pipermail/python-ideas/2015-February/032000.html

[warsaw]

Let's just Won't Fix this. Use a contextlib.ExitStack.