Python 2 scripts do not work starting from Junos 21.1R1.

ZTP or other scripts that run based on Python 2 fail on the newer releases (21.1R1+). 

The Python 2.7 end-of-life and end-of-support date was January 1, 2020, and is no longer supported starting from Junos 21.1R1. The official upgrade path for Python 2.7 is to Python 3.

This documentation provides the release(s) where support for Python 2 was introduced and removed. It also provides the release(s) where the support for Python 3 was added.

Provisioning a Device Using a Python Script (ZTP) that worked on previous releases may fail on release 21.1R1+ if an incompatible syntax is used or the wrong interpreter is referenced.