Why is this an issue?

Functions that use yield are known as "generators". Before Python 3.3, generators cannot return values. Similarly, functions that use return cannot use yield. Doing so will cause a SyntaxError.

Either upgrade your version of Python to a version >= 3.3, or don’t use both return and yield in a function.

Noncompliant code example

def adder(n):
     num = 0
     while num < n:
         yield num
         num += 1
     return num  #Noncompliant