Definitely seems like something that should be warned about.
For python2 it ought to be an error (which can always be turned off) for
either code snippet.
For python3, I'd say the two line snippet should flag an error - yes, it
will fail at run-time, but pydev in eclipse runs pylint and saves me a
lot of grief by spotting this type of thing before I ever save the file
(though it doesn't catch either of these, presumably because they are
valid python).
The three line snippet should probably give a warning ("Are you sure you
mean this?")
The question is, how do we know which version of Python the code under
inspection is targeted for, and hence how to treat this case.
Some thoughts on that:
* Anyone serious enough to be using pyflakes, pylint, or other static
analysis tools is also probably using virtualenv.
* pyflakes is therefore most likely running under the same python
version for which the code is targeted.
* code which is meant to run under multiple python versions is probably
tested under something like tox - so again, pyflakes is run under the
targeted python version (certainly my tox.ini runs it in every target
environment)
There's a lot of "probably"'s in there, but I don't think they are
unreasonable assumptions.
So, could pyflakes reasonably assume that the interpreter under which
it is running is also the intended target version for the code under
inspection? At least for the major version.
This could then be overridden by a suitable command line option to
specify the target version(s)
Also, in cases like this, possibly a "This will behave differently in
Python 2 and 3" warning is a worth while alternative.
Keith Derrick | Principal Engineer, Connected Platform | Engineering
LG Silicon Valley Lab | 5150 Gt America Parkway, Santa Clara, CA 95054
Office: 408.610-5746 | Mobile: 831.383.9567 | LG.com
On 11/26/2014 06:57 AM, Skip Montanaro wrote:
>> That's not the point of this check. The point of this check is that on
>> Python 2, the binding to x in the comprehension bleeds outside of the
>> comprehension scope
> Got it.
>
> Still, this code:
>
>> x = 10
>> [x for x in range(3)]
>> print(x + 1)
> will run differently in Python 2 than Python3, so even if that was a
> conscious choice by the author, a --py3k flag should cause a message
> for this code. This is even worse than the simpler
>
>> [x for x in range(3)]
>> print(x + 1)
> because at least that will raise a NameError when run in Python 3. The
> three-line construct will still run, though produce different output.
>
> Skip
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