Re: [Python-Dev] __future__ and eval()

Ah, interesting! Thanks for the clarification. So it is really possible to write code with an implicit future statement in it, or to switch the behavior off. Good to know. I will probably not use it, since I can't decide on a good default, but getting rid of print_statement is tempting...

https://docs.python.org/2/reference/simple_stmts.html#the-exec-statement

[2] When strings are executed, __future__ directives active in the surrounding context will be active for the compiled code also. If this is not desired, see the compile() function's dont_inherit parameter.

Would that clarify?

Yes please, that would be a good place to document it. For some reason I did not look up __future__. Thanks -- Chris On 01/10/16 14:17, Chris Angelico wrote:

On Sat, Oct 1, 2016 at 9:39 PM, Christian Tismer wrote:

...

The exec() script inherited the __future__ statement! It behaved like the future statement were implicitly there.

Is that a bug or a feature?

It's documented, but not very noisily.

https://docs.python.org/2/reference/simple_stmts.html#future-statements

So if you want to isolate the execution environments, you can use compile() explicitly. Without isolation:

Python 2.7.12+ (default, Sep 1 2016, 20:27:38) [GCC 6.2.0 20160822] on linux2 Type "help", "copyright", "credits" or "license" for more information.

...

...

...

exec(compile("print('hello','world')", "-", "exec")) ('hello', 'world') exec(compile("from __future__ import print_function; print('hello','world')", "-", "exec")) hello world from __future__ import print_function exec(compile("print('hello','world')", "-", "exec")) hello world exec(compile("from __future__ import print_function; print('hello','world')", "-", "exec")) hello world

With isolation:

...

...

...

exec(compile("print('hello','world')", "-", "exec", 0, 1)) ('hello', 'world') exec(compile("from __future__ import print_function; print('hello','world')", "-", "exec", 0, 1)) hello world

So I'd call it a feature, but possibly one that warrants a mention in the exec and eval docs. Maybe something like:

https://docs.python.org/2/reference/simple_stmts.html#the-exec-statement

[2] When strings are executed, __future__ directives active in the surrounding context will be active for the compiled code also. If this is not desired, see the compile() function's dont_inherit parameter.

Would that clarify?

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