Does ROS2 require Python3?

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This is documented in the ROS2 Developers Guide, specifically the Language Versions and Code Format - Python section:

We will target Python 3 for our development.

and also the Changes between ROS 1 and ROS 2 article on design.ros2.org, section Platforms and dependencies - Languages - Python, which is more specific:

ROS 1 is targeting Python 2. ROS 2 requires at least Python version 3.5.