YANG is a data modeling language for NETCONF (RFC4741), developed by the IETF NETMOD WG.
pyang is a YANG validator, transformator and code generator, written in python. It can be used to validate YANG modules for correctness, to transform YANG modules into other formats, and to generate code from the modules.
pyang is compatible with http://www.ietf.org/internet-drafts/draft-ietf-netmod-yang-02.txt.
These details are provided for information only. No information here is legal advice and should not be used as such.