accept python2 print syntax in python 3 files

[jpinon]

Using pyflakes 8.1 on this code does not raise error :

import sys
print >>sys.stderr, "Hello"

Launched with :

python3 -m pyflakes hello.py

[asmeurer (asmeurer)]

It's valid syntax in Python 3. >> is the right shift operator, and the comma creates a tuple. If you run the code, you'll see that it raises a TypeError, not a SyntaxError. Unless pyflakes is going to do some basic operator type checking on builtins (could be a good idea?) it's not going to detect this.

[John Vandenberg (jayvdb)]

fwiw, flake8 plugin `hacking` emits:

H233 Python 3.x incompatible use of print operator

and `flake8-print` emits

T001 print statement found.

It seems reasonable and straight forward for pyflakes to also detect this on Python 3 only.

However, to do this right, pyflakes needs an accurate understanding of `__future__.print_function` so that the error also occurs on Python 2 when `print_function` is active. That should be fairly easy also now, as __future__ in doctest is now correctly detected (see https://github.com/pyflakes/pyflakes/commit/9c88c0ec3f4cdb0fb2e69c2bdadc0bdd03da4a55 ).