New submission from Matthias Bussonnier <bussonniermatthias@gmail.com>: In recent Python the following

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from ast import PyCF_ONLY_AST compile("'a'", 'whatever', 'exec', PyCF_ONLY_AST).body

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 `compile` says:

... it can be 'exec' if source consists of a sequence of statements,

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 `exec` docs. I could argue that now the `exec` name may be a tiny bit unsuitable for the new behavior, and would love if this could be optional. 1: https://github.com/ipython/ipython/issues/11133#issuecomment-388591332 ---------- assignee: docs@python components: Documentation, Interpreter Core messages: 316441 nosy: docs@python, mbussonn priority: normal severity: normal status: open title: Document that compile(code, 'exec') has different behavior in 3.7+ versions: Python 3.7, Python 3.8 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue33477> _______________________________________