Writing a DEX smart contract

Let’s start by creating an Ape project. You should follow these steps:

$ mkdir dex
$ cd dex
$ python3 -m venv .venv
$ source .venv/bin/activate
(.venv) $ pip install eth-ape'[recommended-plugins]'==0.7.23
(.venv) $ ape init
Please enter project name: DEX
SUCCESS: DEX is written in ape-config.yaml

The full code of the DEX smart contract can be found at this URL: https://github.com/PacktPublishing/Hands-On-Blockchain-for-Python-Developers--2nd-Edition/blob/main/chapter_16/dex/contracts/DEX.vy. You can download it and place the smart contract file inside the contracts folder.

But let’s create a smart contract from scratch. Create a new file named DEX.vy inside the contracts folder, then add the following code:

#pragma version ^0.3.0
# Based on https://jeiwan.net/posts/programming-defi-uniswap-1/
from vyper.interfaces import ERC20 as IERC20

The pragma line constrains the version of the Vyper compiler that can compile this...