Read up on the Python 2.x to 3.x forward compatibility. There's a 2to3 program that does a stupendous job of taking your Python 2.x script and making it 3.x compatible if you follow Python's rules & standards for Py 2.x
Should you try writing your python scripts so they will run on both python 2.7 and python 3? For example, in scripts that pull html using urllib2 in Python 2.7, should you use the os module and if statements, to pull using urllib2 if python 2.7 and requests if python 3?
Yeah for many things, 2to3 works quite well. Of course if you use 2.x only libs you are stuck. And of course for some things it is very difficult... Armin Ronacher just did a followup on his experiences porting Jinja2 to Python3 which covers lots of potential problems.