[FIXED] Can a from __future__ import ... guarantee Python 2 and 3 compatibility?

Issue

I'm not interested in warming up the "Python 2 or Python 3?" questions (even though the most recent one I found is over one year old), but I stumbled upon this claim:

You can write the Python 3 code under Python 2 if your file begins with the line:

from __future__ import absolute_import, division, generators, unicode_literals, print_function, nested_scopes, with_statement

With that line in place, your code will work with either Python 2 or Python 3. There may be rare cases in which it doesn't work, but I have not found any,

Is this true? Is this single line enough to make sure the code you write will run on both Python 2.x (>=2.5 I assume) and 3.x (assuming the modules imported are available in both)?

Solution

"It depends"

No: Adding these imports to your Python 2 code will not make it run under Python 3.

Yes: With these imports in place you can write code that runs under both Python 2 and Python 3.

But: Then again, you can do that without those imports as well, and several of them, such as unicode_literals have turned out to simply not be helpful. generators and with_statement have nothing to do with Python 2 to Python 3 at all, those are features added in versions of Python 2.

So in conclusion, these imports are a bit of a red herring, and the statement is more wrong than right.

However, that doesn't mean writing code that runs under both Python 2 and Python 3 is impossible, or even necessarily very hard. See http://python3porting.com/ for more info.

Answered By - Lennart Regebro