Описание тега yield-from
"yield from" is an expression in Python for delegating to a subgenerator.
The expression yield from was added in Python-3.3 based on PEP 380: Syntax for Delegating to a Subgenerator.
In the simplest case it can be used as a shorthand for iterating over a subgenerator, i.e.
for item in sth:
yield item
can be replaced with:
yield from sth