Yes, you can just use lambda expressions. They are made for this.
iterator(lambda x: x/4+12, 100, 5) Words from the docs:
Lambdas are usually used to create small, anonymous functions. Actually, they are just a syntatic sugar to define functions. The lambda expression above is exactly the same as your function, only without a name.
If you wish to learn more, Here is some good read:
http://www.diveintopython.net/power_of_introspection/lambda_functions.html
Why use lambda functions?Why use lambda functions?