https://docs.python.org/3/reference/expressions.html

in
6.2.9. Yield expressions

end of 1st paragraph:

"Using a yield expression in a function’s body causes that function to be a generator."

NO!

As the very next sentence explains, a generator is what's returned by such a function, not the function itself.

Basically, it should be sufficient to add the word "function" to the end of that sentence: "... generator function."  However, this error does NOT exist in 3.0 to 3.2 - just in 3.3 to 3.6, so I suggest just using the same wording as 3.0 to 3.2:

"Using a yield expression in a function definition is sufficient to cause that definition to create a generator function instead of a normal function."