## Introduction to Vyper Modules We're going to be learning about Vyper modules. We'll create a new file called `five_more.vy`. It's going to be very similar to the `favorites.vy` contract, but we'll modify the `store()` function to add five to the number stored. ```python self.my_favorite_number = new_number + 5 ``` We want to reuse as much code as possible without copy-pasting everything, so we'll use Vyper's module system. A module is a way to encapsulate reusable code. Vyper favors **composition over inheritance** - we compose modules to create new contracts. Our `favorites_factory.vy` contract imports the `I_favorites` module: ```python from interfaces import I_favorites ``` The `I_favorites` module helps us type our list of `favorites` contracts. ```python list_of_favorite_contracts: public(DynArray[I_favorites, 100]) ``` When we import a module, it doesn't automatically become part of our contract. We need to explicitly tell Vyper how to use it. We can import the `favorites` contract into our `five_more.vy` file: ```python import favorites ``` Now, if we comment out the variables and functions that we imported, the contract still compiles because we only imported it, not copied it. ```python # my_favorite_number: uint256 # @external # def store(new_number: uint256): # self.my_favorite_number = new_number ``` We can verify this by running the following commands: ```bash mox compile ``` The ABI of our `five_more.vy` contract will be empty since we're just importing it. ```bash # mox run deploy ```