In this lesson we will learn how to build a view function. Firstly, let's go ahead and make a function that returns a value. ```python @external def retrieve() -> uint256: return self.my_favorite_number ``` Then we save and redeploy this: ```bash favorites --favorites.vy ``` Now we will comment out the store function for now. ```python # @external # def store(new_number: uint256): # self.my_favorite_number = new_number ``` We can now see the value returned in the UI: ```bash my_favorite_number --call ``` We will now change the retrieve function to return a value: ```python @external def retrieve() -> uint256: return self.my_favorite_number ``` This time we will redeploy and check the UI: ```bash favorites --favorites.vy ``` Now, if we want to explicitly tell the compiler that this is not a transaction we can simply add the @view decorator to the function: ```python @external @view def retrieve() -> uint256: return self.my_favorite_number ``` Let's redeploy and see what happens in the UI. ```bash favorites --favorites.vy ``` The UI will now display a blue button, indicating that the function is a view function. We will now create a second view function which we will call 'retrieve', and we will also include a note within our code explaining how view functions work. ```python @external def store(new_number: uint256): self.my_favorite_number = new_number @external @view def retrieve() -> uint256: return self.my_favorite_number # a view function can be called # by a human for free -- no gas # but when a transaction calls # a view function, it costs gas @external def store(new_number: uint256): self.my_favorite_number = new_number @internal @view def retrieve() -> uint256: return self.my_favorite_number ``` Next, we will make the retrieve function an external function, so that we can call it. We will also add a few extra retrieve functions, just to highlight the gas cost differences. ```python @external def store(new_number: uint256): self.my_favorite_number = new_number self.retrieve() self.retrieve() self.retrieve() self.retrieve() @internal @view def retrieve() -> uint256: return self.my_favorite_number ``` Let's redeploy and see the difference in gas cost between the view function and external retrieve function. ```bash favorites --favorites.vy ``` If you recall, calling a view function from the UI requires no gas. However, if another transaction calls a view function, then it will incur a gas cost. Calling a view function from the UI is essentially the same as calling the 'public' function.