Retrieve a price with a bot in Python

How to retrieve the price of an asset with a bot on a DEX (Pangolin)

Installing web3.py

Just run this code in your terminal (you may need to run pip3 depending on your installation)

$ pip install web3

Connecting web3

We create a new file : bot.py on which we import our module

bot.py

from web3 import Web3

And we connect to our Web3 provider : Here i have my own node running at this address but you can connect another one as figment.io

Own node

w3 = Web3(Web3.HTTPProvider('http://127.0.0.1:9650/ext/bc/C/rpc'))

Figment.io

Retrieving informations from pool contract

First we need to instantiate a contract object representing the liquidity pool from which we query the price data :

liquidityContract = w3.eth.contract(address=address, abi=abi)

In this example we will look at AVAX price and we will take the WAVAX / USDT pool on pangolin at this address : 0x9ee0a4e21bd333a6bb2ab298194320b8daa26516

In order to make requests to a contract we need its ABI, it's like a definition of its functions and variables in JSON format.

To retrieve it you can go on : https://cchain.explorer.avax.network/address/0x9EE0a4E21bd333a6bb2ab298194320b8DaA26516/contracts and click copy ABI.

You can paste it on a new file : pool.json

Now we can read it from our python script (we also need to import the json module)

import json

with open("Pool.json") as poolFile :
    poolABI = json.load(poolFile )

We need to transform our address to a Checksum valid address or web3.py won't accept it. Our program is now :

bot.py

from web3 import Web3
import json

w3 = Web3(Web3.HTTPProvider('http://127.0.0.1:9650/ext/bc/C/rpc'))

with open("Pool.json") as poolFile :
    poolABI = json.load(poolFile )

liquidityContract = w3.eth.contract(address=w3.toChecksumAddress("0x9ee0a4e21bd333a6bb2ab298194320b8daa26516"), abi=poolABI)

Now we need to make a call to retrieve reserves of each token on this pool (It exists two types of call to a contract one which just read on the blockchain the informations : we call it with .call() and another one which write and really interact with the blockchain : we call it with .transact() )

reserves = liquidityContract.functions.getReserves().call()
reserveToken0 = reserves[0]
reserveToken1 = reserves[1]

The function returns a list of 3 : reserveToken0 , reserveToken1 and timestamp of last update. Our problem is we don't know which of token0 or token1 is WAVAX or USDT we could check manually but we want our bot to work even with other pool in unknown orders so we need to check which one is which.

token0Address = liquidityContract.functions.token0().call()
token1Address = liquidityContract.functions.token1().call()

Retrieving informations from tokens contracts

Now that we have the address of which we can query the blockchain to determine who they are. In order to do so we need to instantiate a contract for each of them and for that we need their ABIs. We just need a basic ERC20 ABI so we're gonna grab one from the explorer (like here : https://cchain.explorer.avax.network/address/0xB31f66AA3C1e785363F0875A1B74E27b85FD66c7/contracts )

We copy paste the ABI in ERC20.json and we load it on python.

with open("ERC20.json") as erc20File:
    ERC20ABI = json.load(erc20File)

Now we can create our contracts instances

token0 = w3.eth.contract(address=w3.toChecksumAddress(token0Address), abi=ERC20ABI)
token1 = w3.eth.contract(address=w3.toChecksumAddress(token1Address), abi=ERC20ABI)

And search for symbols and decimals

token0Symbol = token0.functions.symbol().call()
token0Decimals = token0.functions.decimals().call()

token1Symbol = token1.functions.symbol().call()
token1Decimals = token1.functions.decimals().call()

Calculating results

And now we can calculate the price of (W)AVAX :

if token0Symbol == "WAVAX" :
    price = reserveToken1/10**token1Decimals / reserveToken0/10**token0Decimals
else :
    price = reserveToken0/10**token0Decimals / reserveToken1/10**token1Decimals
print("The current price of AVAX is {:4.2f} USDT".format(price)

Final code

bot.py

from web3 import Web3
import json

w3 = Web3(Web3.HTTPProvider('http://127.0.0.1:9650/ext/bc/C/rpc'))

with open("pool.json") as poolFile :
    poolABI = json.load(poolFile )
with open("ERC20.json") as erc20File:
    ERC20ABI = json.load(erc20File)

liquidityContract = w3.eth.contract(address=w3.toChecksumAddress("0x9ee0a4e21bd333a6bb2ab298194320b8daa26516"), abi=poolABI)

reserves = liquidityContract.functions.getReserves().call()
reserveToken0 = reserves[0]
reserveToken1 = reserves[1]

token0Address = liquidityContract.functions.token0().call()
token1Address = liquidityContract.functions.token1().call()

token0 = w3.eth.contract(address=w3.toChecksumAddress(token0Address), abi=ERC20ABI)
token1 = w3.eth.contract(address=w3.toChecksumAddress(token1Address), abi=ERC20ABI)

token0Symbol = token0.functions.symbol().call()
token0Decimals = token0.functions.decimals().call()

token1Symbol = token1.functions.symbol().call()
token1Decimals = token1.functions.decimals().call()


if token0Symbol == "WAVAX" :
    price = (reserveToken1/10**token1Decimals) / (reserveToken0/10**token0Decimals)
else :
    price = (reserveToken0/10**token0Decimals) / (reserveToken1/10**token1Decimals)
print("The current price of AVAX is {:4.2f} USDT".format(price))