A major motivation for the new syntax is to support refactoring (currently moving "yield" into a sub-function makes the calling function no longer a generator).

See the PEP's "rationale and goals"[1] and this article[2] summarising the PEP.

[1] https://www.python.org/dev/peps/pep-0492/#rationale-and-goal... [2] https://lwn.net/Articles/643786/