On Sat, Oct 1, 2016 at 9:39 PM, Christian Tismer <tismer at stackless.com> 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?
ChrisA
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