Sure, as long as it doesn't contain any syntax or spellings which are incompatible between the two. That's a fairly large subset of the language.
> if you bring a Python2 script and feed it to a Python3 interpreter, no, in general that will not work. They simply aren't the same language. Even a simple "print x" will do you in.
But this will work:
from __future__ import print_function
print(x)
Also, as I said above, there is a pretty large subset of the Python language that has the same syntax and spellings in both Python 2 and Python 3, and any script or module or package that only uses that subset will run just fine under both interpreters. You are drastically underestimating both the size and the usage of this subset of the language.
Yes you often need some precautions like "from __future__ import" statements and sometimes libraries like `six`, but it's been perfectly normal practice for most of the last decade.
In fact, the vast majority of popular libs had a 2/3 compatible code base for a few years.
The hard part was not the syntax in fact. It's pretty trivial: the language are not that different.
The hard part is the I/O stack, because the stdlib is very different, espacially for this part.
Nearly every py3 feature was backported to 2 you just need to write it in a compatible way. I'm seeing some drop py2 support now though. Which I'm fine with, I haven't written python2 code in maybe 6 or 7 years now.
Googling quickly, I find this, which does a bit better than 2to3. I suppose one could write to a somewhat constrained intersection of Python2 and Python3, if one is willing to make at least some boilerplate changes to the original Python2 code.
https://python-future.org/overview.html
That said, if you bring a Python2 script and feed it to a Python3 interpreter, no, in general that will not work. They simply aren't the same language. Even a simple "print x" will do you in.