How to detect Python Version 2 or 3 in script?

sys.version_info provides the version of the used Python interpreter.

Python 2

>>> import sys
>>> sys.version_info
sys.version_info(major=2, minor=7, micro=6, releaselevel='final', serial=0)
>>> sys.version_info[0]
2

Python 3

>>> import sys
>>> sys.version_info
sys.version_info(major=3, minor=7, micro=10, releaselevel='final', serial=0)
>>> sys.version_info[0]
3

For details see the documentation.

You can use the six library (https://pythonhosted.org/six/) to make it easier to write code that works on both versions. (It includes two booleans six.PY2 and six.PY3 which indicate whether the code is running in Python 2 or Python 3)

Also in Python 2.6 and 2.7, you can use

from __future__ import (print_function, unicode_literals, division)
__metaclass__ = type

to enable some of the Python 3 behaviour in a way that works on both 2 and 3.