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Document that compile(code, 'exec') has different behavior in 3.7+ #77658
Description
| BPO | 33477 |
|---|---|
| Nosy | @methane, @Carreau |
| PRs |
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 = None
closed_at = <Date 2018-06-05.18:28:22.638>
created_at = <Date 2018-05-13.00:57:30.375>
labels = ['interpreter-core', '3.7', '3.8', 'docs']
title = "Document that compile(code, 'exec') has different behavior in 3.7+"
updated_at = <Date 2018-06-05.18:28:22.636>
user = 'https://github.com/Carreau'bugs.python.org fields:
activity = <Date 2018-06-05.18:28:22.636>
actor = 'mbussonn'
assignee = 'docs@python'
closed = True
closed_date = <Date 2018-06-05.18:28:22.638>
closer = 'mbussonn'
components = ['Documentation', 'Interpreter Core']
creation = <Date 2018-05-13.00:57:30.375>
creator = 'mbussonn'
dependencies = []
files = []
hgrepos = []
issue_num = 33477
keywords = ['patch']
message_count = 5.0
messages = ['316441', '316490', '317036', '317037', '318779']
nosy_count = 3.0
nosy_names = ['methane', 'docs@python', 'mbussonn']
pr_nums = ['6973']
priority = 'normal'
resolution = None
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue33477'
versions = ['Python 3.7', 'Python 3.8']
Activity
Carreau commentedon May 13, 2018
In recent Python the following
In 3.6 it return
[<_ast.Expr at 0x10b7441d0>] # that contail Str('a')
While on master:
[]
This is inconveninent for alternative repl like IPython, where basically if the user is entering a single string, the result is nothing in Python 3.7+, while it _does_ return something on earlier Python [1].
The documentation of
compilesays:Which is not technically true any more as the first statement, if a string, will be removed.
What's happening here is that since Python 3.7 if the _first_ statement is actually an expression containing a lonely string it is assign to the module docstring. So that's basically assuming you are parsing a module, and that the docstring make sens in this context, while in a REPL you are parsing a sucesssion of statements, in which case there is no need for a docstring that make no sens in this context.
This is _usually_ not an issue, unless this lonely statement is also the last, and what the user wants to execute in a REPL, in which case it has no side effect.
I don't have any objection to the new behavior, though I was wondering if this kind of side effect was anticipated.
If that affect IPython, it will likely effect other alternative REPLs.
Thus, I believe it would be good to have this at least documented a tiny bit better and added in what's new, and potentially clarified in the
execdocs.I could argue that now the
execname may be a tiny bit unsuitable for the new behavior, and would love if this could be optional.1: ipython/ipython#11133 (comment)
methane commentedon May 14, 2018
ref bpo-32911
And it's documented already.
https://docs.python.org/3.7/whatsnew/3.7.html#changes-in-the-python-api
methane commentedon May 18, 2018
Any comments?
Would you close this issue?
Carreau commentedon May 18, 2018
Fair enough that what's new include things about Module
Note that this sentence read backward to me. I understand what is meant because I know the new behavior. It might be good to clarify. potentially:
Though the documentation of
compile()does not say thatcompile(...,'exec')compile a module. It says:Which now is incorrect. I was expecting
compile(..., 'exec')to return a Module withNoneor empty string as the docstring attribute – which is also a perfectly reasonable request.I think that
compiledocumentation should be changed to reflect what it does.Or (but I see why this is un-reasonable) split add the
mode='module'that has new behavior, whileexecdoes not.Carreau commentedon Jun 5, 2018
Closing as the ast changes have been reverted.