In this tutorial we will query the Ethereum mempool using Web3.py in Python. The mempool is also known as the transaction pool and or the txpool. This process and code below will work with all EVM (Ethereum Virtual Machine) compatible blockchains (Ethereum, Optimism, BSC, Polygon, Kucoin Chain, Fantom, etc.).
What is the mempool / txpool
When a transaction is sent to the blockchain it is received by an Ethereum node. This Ethereum node propagates the transaction to other peer Ethereum nodes. While the transaction is waiting to be added to the next block it resides in a staging area called the mempool / txpool. This staging area contains a list of all “pending transactions”. Once the transaction is added to the next block it is considered a confirmed transaction.
- Transactions from different wallets, applications, etc. are submitted to the blockchain for processing.
- These transactions are pending and ordered in the mempool / txpool.
- Mempool / txpool transactions are included in the next block on the blockchain.
This is how a blockchain node deals with transactions that have not yet been included in a block. Pending transactions in the mempool / txpool are a good indication of what is going to happen next on the blockchain. Examining transactions in the mempool will give you additional information that you might need when trading, building applications, watching addresses, etc.
Connect to the blockchain
In order to connect to a blockchain you can use your own node, Quick Node, Chainstack, or any other service. Setting up an account on Chainstack and Quick Node is fast, easy and sometimes free (depending on the service you choose). We attempted to query the mempool with Python using Infura but the process in this tutorial is not supported. As mentioned this process will work with any EVM compatible blockchain so for this tutorial we will focus on Ethereum. After setting up your node be sure to make note of your Ethereum node credentials as you will need to include them in the Python code below.
Setup your Python environment
In this tutorial we will use a virtual environment and Web3.py libraries to query the Ethereum mempool with Python. First setup a virtual environment using your terminal window in your IDE. Then install the Web3.py libraries using PIP install. For more information on how to download Web3.py read here. Finally get your web socket node credentials ready as you will need to include them in the code below.
Query the Ethereum mempool with Python
Some of the sample code below was taken from Web3.py read the docs single threaded concurrency with asyn and await in the filtering section. Then we modified the code to suit our use case.
Copy the code below to query the Ethereum mempool with Python. Read the comments in the code to understand how the code functions. Make sure you enter your web socket node credentials.
from web3.auto import Web3
import asyncio
import json
# enter your web socket node credentials here
# this will allow us to stream transactions
wss = 'wss://EnterYourWSSInformationHere'
web3 = Web3(Web3.WebsocketProvider(wss))
# test to see if you are connected to your node
# this will print out True if you are successfully connected to a node
print(web3.isConnected())
def handle_event(event):
# print the transaction hash
# print(Web3.toJSON(event))
# use a try / except to have the program continue if there is a bad transaction in the list
try:
# remove the quotes in the transaction hash
transaction = Web3.toJSON(event).strip('"')
# use the transaction hash that we removed the '"' from to get the details of the transaction
transaction = web3.eth.get_transaction(transaction)
# print the transaction and its details
print(transaction)
except Exception as err:
# print transactions with errors. Expect to see transactions people submitted with errors
print(f'error: {err}')
async def log_loop(event_filter, poll_interval):
while True:
for event in event_filter.get_new_entries():
handle_event(event)
await asyncio.sleep(poll_interval)
def main():
# filter for pending transactions
tx_filter = web3.eth.filter('pending')
loop = asyncio.get_event_loop()
try:
loop.run_until_complete(
asyncio.gather(
log_loop(tx_filter, 2)))
finally:
loop.close()
if __name__ == '__main__':
main()
Filter mempool for Uniswap or Pancake Swap transactions with Python
In addition, if you would like to take it a step farther and filter the mempool / txpool with Python for transactions only going to Uniswap or Pancake Swap try the code below. A variable called “router” and an “if” condition was added to the try block.
from web3.auto import Web3
import asyncio
import json
# enter your node credentials here
wss = 'wss://EnterYourWSSInformationHere'
web3 = Web3(Web3.WebsocketProvider(wss))
# Check to see if you are connected to your node
print(web3.isConnected())
# add an address you want to filter pending transactions for
# make sure the address is in the correct format
router = web3.toChecksumAddress('EnterUniswapOrPancakeSwapRouterAddressHere')
def handle_event(event):
try:
# remove the quotes in the transaction hash
transaction = Web3.toJSON(event).strip('"')
# use the transaction hash (that we removed the '"' from to get the details of the transaction
transaction = web3.eth.get_transaction(transaction)
# set the variable to the "to" address in the message
to = transaction['to']
# if the to address in the message is the router
if to == router:
# print the transaction and its details
print(transaction)
else:
print('Not what we are looking for')
except Exception as err:
# print transactions with errors. Expect to see transactions people submitted with errors
print(f'error: {err}')
async def log_loop(event_filter, poll_interval):
while True:
for event in event_filter.get_new_entries():
handle_event(event)
await asyncio.sleep(poll_interval)
def main():
# filter for pending transactions
tx_filter = web3.eth.filter('pending')
loop = asyncio.get_event_loop()
try:
loop.run_until_complete(
asyncio.gather(
log_loop(tx_filter, 2)))
finally:
loop.close()
if __name__ == '__main__':
main()Filter mempool for Uniswap or Pancake Swap transaction functions with Python
Finally, for the next part let’s filter for Uniswap or Pancake Swap transactions and see the functions that users are sending to the contracts. With the code below you can filter for transactions sent to the router, see the transactions functions and the details included in the message.
from web3.auto import Web3
import asyncio
import json
# enter your node credentials here
wss = 'wss://EnterYourWSSInformationHere'
web3 = Web3(Web3.WebsocketProvider(wss))
# Check to see if you are connected to your node
print(web3.isConnected())
# add the abi of Uniswap or Pancake Swap
abi = json.loads('[{"inputs":[{"internalType":"address","name":"_factory","type":"address"},{"internalType":"address","name":"_WETH","type":"address"}],"stateMutability":"nonpayable","type":"constructor"},{"inputs":[],"name":"WETH","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"tokenA","type":"address"},{"internalType":"address","name":"tokenB","type":"address"},{"internalType":"uint256","name":"amountADesired","type":"uint256"},{"internalType":"uint256","name":"amountBDesired","type":"uint256"},{"internalType":"uint256","name":"amountAMin","type":"uint256"},{"internalType":"uint256","name":"amountBMin","type":"uint256"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"}],"name":"addLiquidity","outputs":[{"internalType":"uint256","name":"amountA","type":"uint256"},{"internalType":"uint256","name":"amountB","type":"uint256"},{"internalType":"uint256","name":"liquidity","type":"uint256"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"uint256","name":"amountTokenDesired","type":"uint256"},{"internalType":"uint256","name":"amountTokenMin","type":"uint256"},{"internalType":"uint256","name":"amountETHMin","type":"uint256"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"}],"name":"addLiquidityETH","outputs":[{"internalType":"uint256","name":"amountToken","type":"uint256"},{"internalType":"uint256","name":"amountETH","type":"uint256"},{"internalType":"uint256","name":"liquidity","type":"uint256"}],"stateMutability":"payable","type":"function"},{"inputs":[],"name":"factory","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountOut","type":"uint256"},{"internalType":"uint256","name":"reserveIn","type":"uint256"},{"internalType":"uint256","name":"reserveOut","type":"uint256"}],"name":"getAmountIn","outputs":[{"internalType":"uint256","name":"amountIn","type":"uint256"}],"stateMutability":"pure","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountIn","type":"uint256"},{"internalType":"uint256","name":"reserveIn","type":"uint256"},{"internalType":"uint256","name":"reserveOut","type":"uint256"}],"name":"getAmountOut","outputs":[{"internalType":"uint256","name":"amountOut","type":"uint256"}],"stateMutability":"pure","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountOut","type":"uint256"},{"internalType":"address[]","name":"path","type":"address[]"}],"name":"getAmountsIn","outputs":[{"internalType":"uint256[]","name":"amounts","type":"uint256[]"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountIn","type":"uint256"},{"internalType":"address[]","name":"path","type":"address[]"}],"name":"getAmountsOut","outputs":[{"internalType":"uint256[]","name":"amounts","type":"uint256[]"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountA","type":"uint256"},{"internalType":"uint256","name":"reserveA","type":"uint256"},{"internalType":"uint256","name":"reserveB","type":"uint256"}],"name":"quote","outputs":[{"internalType":"uint256","name":"amountB","type":"uint256"}],"stateMutability":"pure","type":"function"},{"inputs":[{"internalType":"address","name":"tokenA","type":"address"},{"internalType":"address","name":"tokenB","type":"address"},{"internalType":"uint256","name":"liquidity","type":"uint256"},{"internalType":"uint256","name":"amountAMin","type":"uint256"},{"internalType":"uint256","name":"amountBMin","type":"uint256"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"}],"name":"removeLiquidity","outputs":[{"internalType":"uint256","name":"amountA","type":"uint256"},{"internalType":"uint256","name":"amountB","type":"uint256"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"uint256","name":"liquidity","type":"uint256"},{"internalType":"uint256","name":"amountTokenMin","type":"uint256"},{"internalType":"uint256","name":"amountETHMin","type":"uint256"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"}],"name":"removeLiquidityETH","outputs":[{"internalType":"uint256","name":"amountToken","type":"uint256"},{"internalType":"uint256","name":"amountETH","type":"uint256"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"uint256","name":"liquidity","type":"uint256"},{"internalType":"uint256","name":"amountTokenMin","type":"uint256"},{"internalType":"uint256","name":"amountETHMin","type":"uint256"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"}],"name":"removeLiquidityETHSupportingFeeOnTransferTokens","outputs":[{"internalType":"uint256","name":"amountETH","type":"uint256"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"uint256","name":"liquidity","type":"uint256"},{"internalType":"uint256","name":"amountTokenMin","type":"uint256"},{"internalType":"uint256","name":"amountETHMin","type":"uint256"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"},{"internalType":"bool","name":"approveMax","type":"bool"},{"internalType":"uint8","name":"v","type":"uint8"},{"internalType":"bytes32","name":"r","type":"bytes32"},{"internalType":"bytes32","name":"s","type":"bytes32"}],"name":"removeLiquidityETHWithPermit","outputs":[{"internalType":"uint256","name":"amountToken","type":"uint256"},{"internalType":"uint256","name":"amountETH","type":"uint256"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"uint256","name":"liquidity","type":"uint256"},{"internalType":"uint256","name":"amountTokenMin","type":"uint256"},{"internalType":"uint256","name":"amountETHMin","type":"uint256"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"},{"internalType":"bool","name":"approveMax","type":"bool"},{"internalType":"uint8","name":"v","type":"uint8"},{"internalType":"bytes32","name":"r","type":"bytes32"},{"internalType":"bytes32","name":"s","type":"bytes32"}],"name":"removeLiquidityETHWithPermitSupportingFeeOnTransferTokens","outputs":[{"internalType":"uint256","name":"amountETH","type":"uint256"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"tokenA","type":"address"},{"internalType":"address","name":"tokenB","type":"address"},{"internalType":"uint256","name":"liquidity","type":"uint256"},{"internalType":"uint256","name":"amountAMin","type":"uint256"},{"internalType":"uint256","name":"amountBMin","type":"uint256"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"},{"internalType":"bool","name":"approveMax","type":"bool"},{"internalType":"uint8","name":"v","type":"uint8"},{"internalType":"bytes32","name":"r","type":"bytes32"},{"internalType":"bytes32","name":"s","type":"bytes32"}],"name":"removeLiquidityWithPermit","outputs":[{"internalType":"uint256","name":"amountA","type":"uint256"},{"internalType":"uint256","name":"amountB","type":"uint256"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountOut","type":"uint256"},{"internalType":"address[]","name":"path","type":"address[]"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"}],"name":"swapETHForExactTokens","outputs":[{"internalType":"uint256[]","name":"amounts","type":"uint256[]"}],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountOutMin","type":"uint256"},{"internalType":"address[]","name":"path","type":"address[]"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"}],"name":"swapExactETHForTokens","outputs":[{"internalType":"uint256[]","name":"amounts","type":"uint256[]"}],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountOutMin","type":"uint256"},{"internalType":"address[]","name":"path","type":"address[]"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"}],"name":"swapExactETHForTokensSupportingFeeOnTransferTokens","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountIn","type":"uint256"},{"internalType":"uint256","name":"amountOutMin","type":"uint256"},{"internalType":"address[]","name":"path","type":"address[]"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"}],"name":"swapExactTokensForETH","outputs":[{"internalType":"uint256[]","name":"amounts","type":"uint256[]"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountIn","type":"uint256"},{"internalType":"uint256","name":"amountOutMin","type":"uint256"},{"internalType":"address[]","name":"path","type":"address[]"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"}],"name":"swapExactTokensForETHSupportingFeeOnTransferTokens","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountIn","type":"uint256"},{"internalType":"uint256","name":"amountOutMin","type":"uint256"},{"internalType":"address[]","name":"path","type":"address[]"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"}],"name":"swapExactTokensForTokens","outputs":[{"internalType":"uint256[]","name":"amounts","type":"uint256[]"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountIn","type":"uint256"},{"internalType":"uint256","name":"amountOutMin","type":"uint256"},{"internalType":"address[]","name":"path","type":"address[]"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"}],"name":"swapExactTokensForTokensSupportingFeeOnTransferTokens","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountOut","type":"uint256"},{"internalType":"uint256","name":"amountInMax","type":"uint256"},{"internalType":"address[]","name":"path","type":"address[]"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"}],"name":"swapTokensForExactETH","outputs":[{"internalType":"uint256[]","name":"amounts","type":"uint256[]"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"amountOut","type":"uint256"},{"internalType":"uint256","name":"amountInMax","type":"uint256"},{"internalType":"address[]","name":"path","type":"address[]"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"deadline","type":"uint256"}],"name":"swapTokensForExactTokens","outputs":[{"internalType":"uint256[]","name":"amounts","type":"uint256[]"}],"stateMutability":"nonpayable","type":"function"},{"stateMutability":"payable","type":"receive"}]')
# add an address you want to filter pending transactions for
# make sure the address is in the correct format
router = web3.toChecksumAddress('0x10ed43c718714eb63d5aa57b78b54704e256024e')
Contract = web3.eth.contract(address=router, abi=abi)
def handle_event(event):
try:
# remove the quotes in the transaction hash
transaction = Web3.toJSON(event).strip('"')
# use the transaction hash (that we removed the '"" from to get the details of the transaction
transaction = web3.eth.get_transaction(transaction)
# set the variable to the "to" address in the message
to = transaction['to']
# get the input data in the transaction message. This tells us what functions are going to be executed on the router
input_data = transaction['input']
# if the to address in the message is the uniswap router
if to == router:
# decode the data so you can read it
decode = Contract.decode_function_input(input_data)
# print the transaction and its details
# you will be able to see the functions that are passed to the router
# try printing the following: for function information use (decode[0]), or for amount in/out use decode[1], or for the path use decode(['path']), or for amountIn use decode('amountIn')
print(decode)
else:
print('Not what we want')
except Exception as err:
# print transactions with errors. Expect to see transactions people submitted with errors
print(f'error: {err}')
async def log_loop(event_filter, poll_interval):
while True:
for event in event_filter.get_new_entries():
handle_event(event)
await asyncio.sleep(poll_interval)
def main():
# filter for pending transactions
tx_filter = web3.eth.filter('pending')
loop = asyncio.get_event_loop()
try:
loop.run_until_complete(
asyncio.gather(
log_loop(tx_filter, 2)))
finally:
loop.close()
if __name__ == '__main__':
main()
Resources
Blockchain Networks
Below is a list of EVM compatible Mainnet and Testnet blockchain networks. Each link contains network configuration, links to multiple faucets for test ETH and tokens, bridge details, and technical resources for each blockchain. Basically everything you need to test and deploy smart contracts or decentralized applications on each chain. For a list of popular Ethereum forums and chat applications click here.
 | Ethereum test network configuration and test ETH faucet information |
 | Optimistic Ethereum Mainnet and Testnet configuration, bridge details, etc. |
 | Polygon network Mainnet and Testnet configuration, faucets for test MATIC tokens, bridge details, etc. |
 | Binance Smart Chain Mainnet and Testnet configuration, faucets for test BNB tokens, bridge details, etc. |
 | Fanton networt Mainnet and Testnet configuration, faucets for test FTM tokens, bridge details, etc. |
 | Kucoin Chain Mainnet and Testnet configuration, faucets for test KCS tokens, bridge details, etc. |
Web3 Software Libraries
You can use the following libraries to interact with an EVM compatible blockchain.
- Python: Web3.py A Python library for interacting with Ethereum. Web3.py examples
- Js: Web3.js Ethereum JavaScript API
- Java: Web3j Web3 Java Ethereum Ðapp API
- PHP: Web3.php A php interface for interacting with the Ethereum blockchain and ecosystem.
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