Here are some common things you might want to do with web3.

Looking up blocks

Blocks can be looked up by either their number or hash using the web3.eth.get_block API. Block hashes should be in their hexadecimal representation. Block numbers

# get a block by number
>>> web3.eth.get_block(12345)
    'author': '0xad5C1768e5974C231b2148169da064e61910f31a',
    'difficulty': 735512610763,
    'extraData': '0x476574682f76312e302e302f6c696e75782f676f312e342e32',
    'gasLimit': 5000,
    'gasUsed': 0,
    'hash': '0x767c2bfb3bdee3f78676c1285cd757bcd5d8c272cef2eb30d9733800a78c0b6d',
    'logsBloom': '0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
    'miner': '0xad5c1768e5974c231b2148169da064e61910f31a',
    'mixHash': '0x31d9ec7e3855aeba37fd92aa1639845e70b360a60f77f12eff530429ef8cfcba',
    'nonce': '0x549f882c5f356f85',
    'number': 12345,
    'parentHash': '0x4b3c1d7e65a507b62734feca1ee9f27a5379e318bd52ae62de7ba67dbeac66a3',
    'receiptsRoot': '0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421',
    'sealFields': ['0x31d9ec7e3855aeba37fd92aa1639845e70b360a60f77f12eff530429ef8cfcba',
    'sha3Uncles': '0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347',
    'size': 539,
    'stateRoot': '0xca495e22ed6b88c61714d129dbc8c94f5bf966ac581c09a57c0a72d0e55e7286',
    'timestamp': 1438367030,
    'totalDifficulty': 3862140487204603,
    'transactions': [],
    'transactionsRoot': '0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421',
    'uncles': [],

# get a block by it's hash
>>> web3.eth.get_block('0x767c2bfb3bdee3f78676c1285cd757bcd5d8c272cef2eb30d9733800a78c0b6d')

Getting the latest block

You can also retrieve the latest block using the string 'latest' in the web3.eth.get_block API.

>>> web3.eth.get_block('latest')

If you want to know the latest block number you can use the web3.eth.block_number property.

>>> web3.eth.block_number

Checking the balance of an account

To find the amount of ether owned by an account, use the get_balance() method. At the time of writing, the account with the most ether has a public address of 0x742d35Cc6634C0532925a3b844Bc454e4438f44e.

>>> web3.eth.get_balance('0x742d35Cc6634C0532925a3b844Bc454e4438f44e')

Note that this number is not denominated in ether, but instead in the smallest unit of value in Ethereum, wei. Read on to learn how to convert that number to ether.

Converting currency denominations

Web3 can help you convert between denominations. The following denominations are supported.

denomination amount in wei
wei 1
kwei 1000
babbage 1000
femtoether 1000
mwei 1000000
lovelace 1000000
picoether 1000000
gwei 1000000000
shannon 1000000000
nanoether 1000000000
nano 1000000000
szabo 1000000000000
microether 1000000000000
micro 1000000000000
finney 1000000000000000
milliether 1000000000000000
milli 1000000000000000
ether 1000000000000000000
kether 1000000000000000000000
grand 1000000000000000000000
mether 1000000000000000000000000
gether 1000000000000000000000000000
tether 1000000000000000000000000000000

Picking up from the previous example, the largest account contained 3841357360894980500000001 wei. You can use the from_wei() method to convert that balance to ether (or another denomination).

>>> web3.from_wei(3841357360894980500000001, 'ether')

To convert back to wei, you can use the inverse function, to_wei(). Note that Python’s default floating point precision is insufficient for this use case, so it’s necessary to cast the value to a Decimal if it isn’t already.

>>> from decimal import Decimal
>>> web3.to_wei(Decimal('3841357.360894980500000001'), 'ether')

Best practice: If you need to work with multiple currency denominations, default to wei. A typical workflow may require a conversion from some denomination to wei, then from wei to whatever you need.

>>> web3.to_wei(Decimal('0.000000005'), 'ether')
>>> web3.from_wei(5000000000, 'gwei')

Making transactions

There are a few options for making transactions:

  • send_transaction()

    Use this method if:
    • you want to send ether from one account to another.
  • send_raw_transaction()

    Use this method if:
    • you want to sign the transaction elsewhere, e.g., a hardware wallet.
    • you want to broadcast a transaction through another provider, e.g., Infura.
    • you have some other advanced use case that requires more flexibility.
  • Contract Functions

    Use these methods if:
    • you want to interact with a contract. Web3.py parses the contract ABI and makes those functions available via the functions property.
  • construct_sign_and_send_raw_middleware()

    Use this middleware if:
    • you want to automate signing when using w3.eth.send_transaction or ContractFunctions.


The location of your keys (e.g., local or hosted) will have implications on these methods. Read about the differences here.

Looking up transactions

You can look up transactions using the web3.eth.get_transaction function.

>>> web3.eth.get_transaction('0x5c504ed432cb51138bcf09aa5e8a410dd4a1e204ef84bfed1be16dfba1b22060')
    'blockHash': '0x4e3a3754410177e6937ef1f84bba68ea139e8d1a2258c5f85db9f1cd715a1bdd',
    'blockNumber': 46147,
    'condition': None,
    'creates': None,
    'from': '0xA1E4380A3B1f749673E270229993eE55F35663b4',
    'gas': 21000,
    'gasPrice': None,
    'hash': '0x5c504ed432cb51138bcf09aa5e8a410dd4a1e204ef84bfed1be16dfba1b22060',
    'input': '0x',
    'maxFeePerGas': 2000000000,
    'maxPriorityFeePerGas': 1000000000,
    'networkId': None,
    'nonce': 0,
    'publicKey': '0x376fc429acc35e610f75b14bc96242b13623833569a5bb3d72c17be7e51da0bb58e48e2462a59897cead8ab88e78709f9d24fd6ec24d1456f43aae407a8970e4',
    'r': '0x88ff6cf0fefd94db46111149ae4bfc179e9b94721fffd821d38d16464b3f71d0',
    'raw': '0xf86780862d79883d2000825208945df9b87991262f6ba471f09758cde1c0fc1de734827a69801ca088ff6cf0fefd94db46111149ae4bfc179e9b94721fffd821d38d16464b3f71d0a045e0aff800961cfce805daef7016b9b675c137a6a41a548f7b60a3484c06a33a',
    's': '0x45e0aff800961cfce805daef7016b9b675c137a6a41a548f7b60a3484c06a33a',
    'standardV': '0x1',
    'to': '0x5DF9B87991262F6BA471F09758CDE1c0FC1De734',
    'transactionIndex': 0,
    'v': '0x1c',
    'value': 31337,

If no transaction for the given hash can be found, then this function will instead return None.

Looking up receipts

Transaction receipts can be retrieved using the web3.eth.get_transaction_receipt API.

>>> web3.eth.get_transaction_receipt('0x5c504ed432cb51138bcf09aa5e8a410dd4a1e204ef84bfed1be16dfba1b22060')
    'blockHash': '0x4e3a3754410177e6937ef1f84bba68ea139e8d1a2258c5f85db9f1cd715a1bdd',
    'blockNumber': 46147,
    'contractAddress': None,
    'cumulativeGasUsed': 21000,
    'gasUsed': 21000,
    'logs': [],
    'logsBloom': '0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
    'root': '0x96a8e009d2b88b1483e6941e6812e32263b05683fac202abc622a3e31aed1957',
    'transactionHash': '0x5c504ed432cb51138bcf09aa5e8a410dd4a1e204ef84bfed1be16dfba1b22060',
    'transactionIndex': 0,

If the transaction has not yet been mined then this method will raise a TransactionNotFound error.

Working with Contracts

Interacting with existing contracts

In order to use an existing contract, you’ll need its deployed address and its ABI. Both can be found using block explorers, like Etherscan. Once you instantiate a contract instance, you can read data and execute transactions.

# Configure w3, e.g., w3 = Web3(...)
address = '0x1f9840a85d5aF5bf1D1762F925BDADdC4201F988'
abi = '[{"inputs":[{"internalType":"address","name":"account","type":"address"},{"internalType":"address","name":"minter_","type":"address"},...'
contract_instance = w3.eth.contract(address=address, abi=abi)

# read state:
# 42

# update state:
tx_hash = contract_instance.functions.updateValue(43).transact()

Deploying new contracts

Given the following solidity source file stored at contract.sol.

contract StoreVar {

    uint8 public _myVar;
    event MyEvent(uint indexed _var);

    function setVar(uint8 _var) public {
        _myVar = _var;
        emit MyEvent(_var);

    function getVar() public view returns (uint8) {
        return _myVar;


The following example demonstrates a few things:

  • Compiling a contract from a sol file.
  • Estimating gas costs of a transaction.
  • Transacting with a contract function.
  • Waiting for a transaction receipt to be mined.
import sys
import time
import pprint

from web3.providers.eth_tester import EthereumTesterProvider
from web3 import Web3
from eth_tester import PyEVMBackend
from solcx import compile_source

def compile_source_file(file_path):
   with open(file_path, 'r') as f:
      source = f.read()

   return compile_source(source)

def deploy_contract(w3, contract_interface):
    tx_hash = w3.eth.contract(

    address = w3.eth.get_transaction_receipt(tx_hash)['contractAddress']
    return address

w3 = Web3(EthereumTesterProvider(PyEVMBackend()))

contract_source_path = 'contract.sol'
compiled_sol = compile_source_file('contract.sol')

contract_id, contract_interface = compiled_sol.popitem()

address = deploy_contract(w3, contract_interface)
print(f'Deployed {contract_id} to: {address}\n')

store_var_contract = w3.eth.contract(address=address, abi=contract_interface["abi"])

gas_estimate = store_var_contract.functions.setVar(255).estimate_gas()
print(f'Gas estimate to transact with setVar: {gas_estimate}')

if gas_estimate < 100000:
     print("Sending transaction to setVar(255)\n")
     tx_hash = store_var_contract.functions.setVar(255).transact()
     receipt = w3.eth.wait_for_transaction_receipt(tx_hash)
     print("Transaction receipt mined:")
     print("\nWas transaction successful?")
     print("Gas cost exceeds 100000")


Deployed <stdin>:StoreVar to: 0xF2E246BB76DF876Cef8b38ae84130F4F55De395b

Gas estimate to transact with setVar: 45535

Sending transaction to setVar(255)

Transaction receipt mined:
{'blockHash': HexBytes('0x837609ad0a404718c131ac5157373662944b778250a507783349d4e78bd8ac84'),
 'blockNumber': 2,
 'contractAddress': None,
 'cumulativeGasUsed': 43488,
 'gasUsed': 43488,
 'logs': [AttributeDict({'type': 'mined', 'logIndex': 0, 'transactionIndex': 0, 'transactionHash': HexBytes('0x50aa3ba0673243f1e60f546a12ab364fc2f6603b1654052ebec2b83d4524c6d0'), 'blockHash': HexBytes('0x837609ad0a404718c131ac5157373662944b778250a507783349d4e78bd8ac84'), 'blockNumber': 2, 'address': '0xF2E246BB76DF876Cef8b38ae84130F4F55De395b', 'data': '0x', 'topics': [HexBytes('0x6c2b4666ba8da5a95717621d879a77de725f3d816709b9cbe9f059b8f875e284'), HexBytes('0x00000000000000000000000000000000000000000000000000000000000000ff')]})],
 'status': 1,
 'transactionHash': HexBytes('0x50aa3ba0673243f1e60f546a12ab364fc2f6603b1654052ebec2b83d4524c6d0'),
 'transactionIndex': 0}

 Was transaction successful?

Working with Contracts via ethPM

ethPM packages contain configured contracts ready for use. Web3’s ethpm module (web3.pm) extends Web3’s native Contract module, with a few modifications for how you instantiate Contract factories and instances.

All you need is the package name, version and ethPM registry address for the package you wish to use. An ethPM registry is an on-chain datastore for the release data associated with an ethPM package. You can find some sample registries to explore in the ethPM registry. Remember, you should only use packages from registries whose maintainer you trust not to inject malicious code!

In this example we will use the ethregistrar@3.0.0 package sourced from the ens.snakecharmers.eth registry.

web3.pm uses the Package class to represent an ethPM package. This object houses all of the contract assets within a package, and exposes them via an API. So, before we can interact with our package, we need to generate it as a Package instance.

from web3.auto.infura import w3

# Note. To use the web3.pm module, you will need to instantiate your w3 instance
# with a web3 provider connected to the chain on which your registry lives.

# The ethPM module is still experimental and subject to change,
# so for now we need to enable it via a temporary flag.

# Then we need to set the registry address that we want to use.
# This should be an ENS address, but can also be a checksummed contract address.

# This generates a Package instance of the target ethPM package.
ens_package = w3.pm.get_package("ethregistrar", "3.0.0")

Now that we have a Package representation of our target ethPM package, we can generate contract factories and instances from this Package. However, it’s important to note that some packages might be missing the necessary contract assets needed to generate an instance or a factory. You can use the ethPM CLI to figure out the available contract types and deployments within an ethPM package.

# To interact with a deployment located in an ethPM package.
# Note. This will only expose deployments located on the
# chain of the connected provider (in this example, mainnet)
mainnet_registrar = ens_package.deployments.get_instance("BaseRegistrarImplementation")

# Now you can treat mainnet_registrar like any other Web3 Contract instance!
> 0

mainnet_registrar.functions.approve("0x123", 100000).transact()
> 0x123abc...  # tx_hash

# To create a contract factory from a contract type located in an ethPM package.
registrar_factory = ens_package.get_contract_factory("BaseRegistrarImplementation")

# Now you can treat registrar_factory like any other Web3 Contract factory to deploy new instances!
# Note. This will deploy new instances to the chain of the connected provider (in this example, mainnet)
> 0x456def...  # tx_hash

# To connect your Package to a new chain - simply pass it a new Web3 instance
# connected to your provider of choice. Now your factories will automatically
# deploy to this new chain, and the deployments available on a package will
# be automatically filtered to those located on the new chain.
from web3.auto.infura.goerli import w3 as goerli_w3
goerli_registrar = ens_package.update_w3(goerli_w3)

Working with an ERC20 Token Contract

Most fungible tokens on the Ethereum blockchain conform to the ERC20 standard. This section of the guide covers interacting with an existing token contract which conforms to this standard.

In this guide we will interact with an existing token contract that we have already deployed to a local testing chain. This guide assumes:

  1. An existing token contract at a known address.
  2. Access to the proper ABI for the given contract.
  3. A web3.main.Web3 instance connected to a provider with an unlocked account which can send transactions.

Creating the contract factory

First we need to create a contract instance with the address of our token contract and the ERC20 ABI.

>>> contract = w3.eth.contract(contract_address, abi=ABI)
>>> contract.address

Querying token metadata

Each token will have a total supply which represents the total number of tokens in circulation. In this example we’ve initialized the token contract to have 1 million tokens. Since this token contract is setup to have 18 decimal places, the raw total supply returned by the contract is going to have 18 additional decimal places.

>>> contract.functions.name().call()
>>> contract.functions.symbol().call()
>>> decimals = contract.functions.decimals().call()
>>> decimals
>>> DECIMALS = 10 ** decimals
>>> contract.functions.totalSupply().call() // DECIMALS

Query account balances

Next we can query some account balances using the contract’s balanceOf function. The token contract we are using starts with a single account which we’ll refer to as alice holding all of the tokens.

>>> alice = '0x7E5F4552091A69125d5DfCb7b8C2659029395Bdf'
>>> bob = '0x2B5AD5c4795c026514f8317c7a215E218DcCD6cF'
>>> raw_balance = contract.functions.balanceOf(alice).call()
>>> raw_balance
>>> raw_balance // DECIMALS
>>> contract.functions.balanceOf(bob).call()

Sending tokens

Next we can transfer some tokens from alice to bob using the contract’s transfer function.

>>> tx_hash = contract.functions.transfer(bob, 100).transact({'from': alice})
>>> tx_receipt = w3.eth.wait_for_transaction_receipt(tx_hash)
>>> contract.functions.balanceOf(alice).call()
>>> contract.functions.balanceOf(bob).call()

Creating an approval for external transfers

Alice could also approve someone else to spend tokens from her account using the approve function. We can also query how many tokens we’re approved to spend using the allowance function.

>>> contract.functions.allowance(alice, bob).call()
>>> tx_hash = contract.functions.approve(bob, 200).transact({'from': alice})
>>> tx_receipt = w3.eth.wait_for_transaction_receipt(tx_hash)
>>> contract.functions.allowance(alice, bob).call()

Performing an external transfer

When someone has an allowance they can transfer those tokens using the transferFrom function.

>>> contract.functions.allowance(alice, bob).call()
>>> contract.functions.balanceOf(bob).call()
>>> tx_hash = contract.functions.transferFrom(alice, bob, 75).transact({'from': bob})
>>> tx_receipt = w3.eth.wait_for_transaction_receipt(tx_hash)
>>> contract.functions.allowance(alice, bob).call()
>>> contract.functions.balanceOf(bob).call()

Contract Unit Tests in Python

Here is an example of how one can use the pytest framework in python, Web3.py, eth-tester, and PyEVM to perform unit tests entirely in python without any additional need for a full featured ethereum node/client. To install needed dependencies you can use the pinned extra for eth_tester in web3 and pytest:

$ pip install web3[tester] pytest

Once you have an environment set up for testing, you can then write your tests like so:

import pytest

from web3 import (

def tester_provider():
    return EthereumTesterProvider()

def eth_tester(tester_provider):
    return tester_provider.ethereum_tester

def w3(tester_provider):
    return Web3(tester_provider)

def foo_contract(eth_tester, w3):
    # For simplicity of this example we statically define the
    # contract code here. You might read your contracts from a
    # file, or something else to test with in your own code
    # pragma solidity^0.5.3;
    # contract Foo {
    #     string public bar;
    #     event barred(string _bar);
    #     constructor() public {
    #         bar = "hello world";
    #     }
    #     function setBar(string memory _bar) public {
    #         bar = _bar;
    #         emit barred(_bar);
    #     }
    # }

    deploy_address = eth_tester.get_accounts()[0]

    abi = """[{"anonymous":false,"inputs":[{"indexed":false,"name":"_bar","type":"string"}],"name":"barred","type":"event"},{"constant":false,"inputs":[{"name":"_bar","type":"string"}],"name":"setBar","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"inputs":[],"payable":false,"stateMutability":"nonpayable","type":"constructor"},{"constant":true,"inputs":[],"name":"bar","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"}]"""  # noqa: E501
    # This bytecode is the output of compiling with
    # solc version:0.5.3+commit.10d17f24.Emscripten.clang
    bytecode = """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"""  # noqa: E501

    # Create our contract class.
    FooContract = w3.eth.contract(abi=abi, bytecode=bytecode)
    # issue a transaction to deploy the contract.
    tx_hash = FooContract.constructor().transact({
        'from': deploy_address,
    # wait for the transaction to be mined
    tx_receipt = w3.eth.wait_for_transaction_receipt(tx_hash, 180)
    # instantiate and return an instance of our contract.
    return FooContract(tx_receipt.contractAddress)

def test_initial_greeting(foo_contract):
    hw = foo_contract.caller.bar()
    assert hw == "hello world"

def test_can_update_greeting(w3, foo_contract):
    # send transaction that updates the greeting
    tx_hash = foo_contract.functions.setBar(
        "testing contracts is easy",
        'from': w3.eth.accounts[1],
    w3.eth.wait_for_transaction_receipt(tx_hash, 180)

    # verify that the contract is now using the updated greeting
    hw = foo_contract.caller.bar()
    assert hw == "testing contracts is easy"

def test_updating_greeting_emits_event(w3, foo_contract):
    # send transaction that updates the greeting
    tx_hash = foo_contract.functions.setBar(
        "testing contracts is easy",
        'from': w3.eth.accounts[1],
    receipt = w3.eth.wait_for_transaction_receipt(tx_hash, 180)

    # get all of the `barred` logs for the contract
    logs = foo_contract.events.barred.get_logs()
    assert len(logs) == 1

    # verify that the log's data matches the expected value
    event = logs[0]
    assert event.blockHash == receipt.blockHash
    assert event.args._bar == "testing contracts is easy"

Using Infura Rinkeby Node

Import your required libraries

from web3 import Web3, HTTPProvider

Initialize a web3 instance with an Infura node

w3 = Web3(Web3.HTTPProvider("https://rinkeby.infura.io/v3/YOUR_INFURA_KEY"))

Inject the middleware into the middleware onion

from web3.middleware import geth_poa_middleware
w3.middleware_onion.inject(geth_poa_middleware, layer=0)

Just remember that you have to sign all transactions locally, as infura does not handle any keys from your wallet ( refer to this )

transaction = contract.functions.function_Name(params).build_transaction()
transaction.update({ 'gas' : appropriate_gas_amount })
transaction.update({ 'nonce' : w3.eth.get_transaction_count('Your_Wallet_Address') })
signed_tx = w3.eth.account.sign_transaction(transaction, private_key)

P.S : the two updates are done to the transaction dictionary, since a raw transaction might not contain gas & nonce amounts, so you have to add them manually.

And finally, send the transaction

txn_hash = w3.eth.send_raw_transaction(signed_tx.rawTransaction)
txn_receipt = w3.eth.wait_for_transaction_receipt(txn_hash)

Tip : afterwards you can use the value stored in txn_hash, in an explorer like etherscan to view the transaction’s details

Adjusting log levels

Web3.py internally uses Python logging subsystem.

If you want to run your application logging in debug mode, below is an example of how to make some JSON-RPC traffic quieter.

import logging
import coloredlogs

def setup_logging(log_level=logging.DEBUG):
    """Setup root logger and quiet some levels."""
    logger = logging.getLogger()

    # Set log format to dislay the logger name to hunt down verbose logging modules
    fmt = "%(name)-25s %(levelname)-8s %(message)s"

    # Use colored logging output for console with the coloredlogs package
    # https://pypi.org/project/coloredlogs/
    coloredlogs.install(level=log_level, fmt=fmt, logger=logger)

    # Disable logging of JSON-RPC requests and replies
    # logging.getLogger("web3.RequestManager").propagate = False

    # Disable all internal debug logging of requests and urllib3
    # E.g. HTTP traffic

    return logger

Advanced example: Fetching all token transfer events

In this example, we show how to fetch all events of a certain event type from the Ethereum blockchain. There are three challenges when working with a large set of events:

  • How to incrementally update an existing database of fetched events
  • How to deal with interruptions in long running processes
  • How to deal with eth_getLogs JSON-RPC call query limitations
  • How to handle Ethereum minor chain reorganisations in (near) real-time data

eth_getLogs limitations

Ethereum JSON-RPC API servers, like Geth, do not provide easy to paginate over events, only over blocks. There’s no request that can find the first block with an event or how many events occur within a range of blocks. The only feedback the JSON-RPC service will give you is whether the eth_getLogs call failed.

In this example script, we provide two kinds of heurestics to deal with this issue. The script scans events in a chunk of blocks (start block number - end block number). Then it uses two methods to find how many events there are likely to be in a block window:

  • Dynamically set the block range window size, while never exceeding a threshold (e.g., 10,000 blocks).
  • In the case eth_getLogs JSON-PRC call gives a timeout error, decrease the end block number and try again with a smaller block range window.

Example code

The following example code is divided into a reusable EventScanner class and then a demo script that:

  • fetches all transfer events for RCC token,
  • can incrementally run again to check if there are new events,
  • handles interruptions (e.g., CTRL+C abort) gracefully,
  • writes all Transfer events in a single file JSON database, so that other process can consume them,
  • uses the tqdm library for progress bar output in a console,
  • only supports HTTPS providers, because JSON-RPC retry logic depends on the implementation details of the underlying protocol,
  • disables the standard http_retry_request_middleware because it does not know how to handle the shrinking block range window for eth_getLogs, and
  • consumes around 20k JSON-RPC API calls.

The script can be run with: python ./eventscanner.py <your JSON-RPC API URL>.

"""A stateful event scanner for Ethereum-based blockchains using Web3.py.

With the stateful mechanism, you can do one batch scan or incremental scans,
where events are added wherever the scanner left off.

import datetime
import time
import logging
from abc import ABC, abstractmethod
from typing import Tuple, Optional, Callable, List, Iterable

from web3 import Web3
from web3.contract import Contract
from web3.datastructures import AttributeDict
from web3.exceptions import BlockNotFound
from eth_abi.codec import ABICodec

# Currently this method is not exposed over official web3 API,
# but we need it to construct eth_getLogs parameters
from web3._utils.filters import construct_event_filter_params
from web3._utils.events import get_event_data

logger = logging.getLogger(__name__)

class EventScannerState(ABC):
    """Application state that remembers what blocks we have scanned in the case of crash.

    def get_last_scanned_block(self) -> int:
        """Number of the last block we have scanned on the previous cycle.

        :return: 0 if no blocks scanned yet

    def start_chunk(self, block_number: int):
        """Scanner is about to ask data of multiple blocks over JSON-RPC.

        Start a database session if needed.

    def end_chunk(self, block_number: int):
        """Scanner finished a number of blocks.

        Persistent any data in your state now.

    def process_event(self, block_when: datetime.datetime, event: AttributeDict) -> object:
        """Process incoming events.

        This function takes raw events from Web3, transforms them to your application internal
        format, then saves them in a database or some other state.

        :param block_when: When this block was mined

        :param event: Symbolic dictionary of the event data

        :return: Internal state structure that is the result of event tranformation.

    def delete_data(self, since_block: int) -> int:
        """Delete any data since this block was scanned.

        Purges any potential minor reorg data.

class EventScanner:
    """Scan blockchain for events and try not to abuse JSON-RPC API too much.

    Can be used for real-time scans, as it detects minor chain reorganisation and rescans.
    Unlike the easy web3.contract.Contract, this scanner can scan events from multiple contracts at once.
    For example, you can get all transfers from all tokens in the same scan.

    You *should* disable the default `http_retry_request_middleware` on your provider for Web3,
    because it cannot correctly throttle and decrease the `eth_getLogs` block number range.

    def __init__(self, web3: Web3, contract: Contract, state: EventScannerState, events: List, filters: {},
                 max_chunk_scan_size: int = 10000, max_request_retries: int = 30, request_retry_seconds: float = 3.0):
        :param contract: Contract
        :param events: List of web3 Event we scan
        :param filters: Filters passed to get_logs
        :param max_chunk_scan_size: JSON-RPC API limit in the number of blocks we query. (Recommendation: 10,000 for mainnet, 500,000 for testnets)
        :param max_request_retries: How many times we try to reattempt a failed JSON-RPC call
        :param request_retry_seconds: Delay between failed requests to let JSON-RPC server to recover

        self.logger = logger
        self.contract = contract
        self.web3 = web3
        self.state = state
        self.events = events
        self.filters = filters

        # Our JSON-RPC throttling parameters
        self.min_scan_chunk_size = 10  # 12 s/block = 120 seconds period
        self.max_scan_chunk_size = max_chunk_scan_size
        self.max_request_retries = max_request_retries
        self.request_retry_seconds = request_retry_seconds

        # Factor how fast we increase the chunk size if results are found
        # # (slow down scan after starting to get hits)
        self.chunk_size_decrease = 0.5

        # Factor how was we increase chunk size if no results found
        self.chunk_size_increase = 2.0

    def address(self):
        return self.token_address

    def get_block_timestamp(self, block_num) -> datetime.datetime:
        """Get Ethereum block timestamp"""
            block_info = self.web3.eth.getBlock(block_num)
        except BlockNotFound:
            # Block was not mined yet,
            # minor chain reorganisation?
            return None
        last_time = block_info["timestamp"]
        return datetime.datetime.utcfromtimestamp(last_time)

    def get_suggested_scan_start_block(self):
        """Get where we should start to scan for new token events.

        If there are no prior scans, start from block 1.
        Otherwise, start from the last end block minus ten blocks.
        We rescan the last ten scanned blocks in the case there were forks to avoid
        misaccounting due to minor single block works (happens once in a hour in Ethereum).
        These heurestics could be made more robust, but this is for the sake of simple reference implementation.

        end_block = self.get_last_scanned_block()
        if end_block:
            return max(1, end_block - self.NUM_BLOCKS_RESCAN_FOR_FORKS)
        return 1

    def get_suggested_scan_end_block(self):
        """Get the last mined block on Ethereum chain we are following."""

        # Do not scan all the way to the final block, as this
        # block might not be mined yet
        return self.web3.eth.blockNumber - 1

    def get_last_scanned_block(self) -> int:
        return self.state.get_last_scanned_block()

    def delete_potentially_forked_block_data(self, after_block: int):
        """Purge old data in the case of blockchain reorganisation."""

    def scan_chunk(self, start_block, end_block) -> Tuple[int, datetime.datetime, list]:
        """Read and process events between to block numbers.

        Dynamically decrease the size of the chunk if the case JSON-RPC server pukes out.

        :return: tuple(actual end block number, when this block was mined, processed events)

        block_timestamps = {}
        get_block_timestamp = self.get_block_timestamp

        # Cache block timestamps to reduce some RPC overhead
        # Real solution might include smarter models around block
        def get_block_when(block_num):
            if block_num not in block_timestamps:
                block_timestamps[block_num] = get_block_timestamp(block_num)
            return block_timestamps[block_num]

        all_processed = []

        for event_type in self.events:

            # Callable that takes care of the underlying web3 call
            def _fetch_events(_start_block, _end_block):
                return _fetch_events_for_all_contracts(self.web3,

            # Do `n` retries on `eth_getLogs`,
            # throttle down block range if needed
            end_block, events = _retry_web3_call(

            for evt in events:
                idx = evt["logIndex"]  # Integer of the log index position in the block, null when its pending

                # We cannot avoid minor chain reorganisations, but
                # at least we must avoid blocks that are not mined yet
                assert idx is not None, "Somehow tried to scan a pending block"

                block_number = evt["blockNumber"]

                # Get UTC time when this event happened (block mined timestamp)
                # from our in-memory cache
                block_when = get_block_when(block_number)

                logger.debug("Processing event %s, block:%d count:%d", evt["event"], evt["blockNumber"])
                processed = self.state.process_event(block_when, evt)

        end_block_timestamp = get_block_when(end_block)
        return end_block, end_block_timestamp, all_processed

    def estimate_next_chunk_size(self, current_chuck_size: int, event_found_count: int):
        """Try to figure out optimal chunk size

        Our scanner might need to scan the whole blockchain for all events

        * We want to minimize API calls over empty blocks

        * We want to make sure that one scan chunk does not try to process too many entries once, as we try to control commit buffer size and potentially asynchronous busy loop

        * Do not overload node serving JSON-RPC API by asking data for too many events at a time

        Currently Ethereum JSON-API does not have an API to tell when a first event occurred in a blockchain
        and our heuristics try to accelerate block fetching (chunk size) until we see the first event.

        These heurestics exponentially increase the scan chunk size depending on if we are seeing events or not.
        When any transfers are encountered, we are back to scanning only a few blocks at a time.
        It does not make sense to do a full chain scan starting from block 1, doing one JSON-RPC call per 20 blocks.

        if event_found_count > 0:
            # When we encounter first events, reset the chunk size window
            current_chuck_size = self.min_scan_chunk_size
            current_chuck_size *= self.chunk_size_increase

        current_chuck_size = max(self.min_scan_chunk_size, current_chuck_size)
        current_chuck_size = min(self.max_scan_chunk_size, current_chuck_size)
        return int(current_chuck_size)

    def scan(self, start_block, end_block, start_chunk_size=20, progress_callback=Optional[Callable]) -> Tuple[
        list, int]:
        """Perform a token balances scan.

        Assumes all balances in the database are valid before start_block (no forks sneaked in).

        :param start_block: The first block included in the scan

        :param end_block: The last block included in the scan

        :param start_chunk_size: How many blocks we try to fetch over JSON-RPC on the first attempt

        :param progress_callback: If this is an UI application, update the progress of the scan

        :return: [All processed events, number of chunks used]

        assert start_block <= end_block

        current_block = start_block

        # Scan in chunks, commit between
        chunk_size = start_chunk_size
        last_scan_duration = last_logs_found = 0
        total_chunks_scanned = 0

        # All processed entries we got on this scan cycle
        all_processed = []

        while current_block <= end_block:

            self.state.start_chunk(current_block, chunk_size)

            # Print some diagnostics to logs to try to fiddle with real world JSON-RPC API performance
            estimated_end_block = current_block + chunk_size
                "Scanning token transfers for blocks: %d - %d, chunk size %d, last chunk scan took %f, last logs found %d",
                current_block, estimated_end_block, chunk_size, last_scan_duration, last_logs_found)

            start = time.time()
            actual_end_block, end_block_timestamp, new_entries = self.scan_chunk(current_block, estimated_end_block)

            # Where does our current chunk scan ends - are we out of chain yet?
            current_end = actual_end_block

            last_scan_duration = time.time() - start
            all_processed += new_entries

            # Print progress bar
            if progress_callback:
                progress_callback(start_block, end_block, current_block, end_block_timestamp, chunk_size, len(new_entries))

            # Try to guess how many blocks to fetch over `eth_getLogs` API next time
            chunk_size = self.estimate_next_chunk_size(chunk_size, len(new_entries))

            # Set where the next chunk starts
            current_block = current_end + 1
            total_chunks_scanned += 1

        return all_processed, total_chunks_scanned

def _retry_web3_call(func, start_block, end_block, retries, delay) -> Tuple[int, list]:
    """A custom retry loop to throttle down block range.

    If our JSON-RPC server cannot serve all incoming `eth_getLogs` in a single request,
    we retry and throttle down block range for every retry.

    For example, Go Ethereum does not indicate what is an acceptable response size.
    It just fails on the server-side with a "context was cancelled" warning.

    :param func: A callable that triggers Ethereum JSON-RPC, as func(start_block, end_block)
    :param start_block: The initial start block of the block range
    :param end_block: The initial start block of the block range
    :param retries: How many times we retry
    :param delay: Time to sleep between retries
    for i in range(retries):
            return end_block, func(start_block, end_block)
        except Exception as e:
            # Assume this is HTTPConnectionPool(host='localhost', port=8545): Read timed out. (read timeout=10)
            # from Go Ethereum. This translates to the error "context was cancelled" on the server side:
            # https://github.com/ethereum/go-ethereum/issues/20426
            if i < retries - 1:
                # Give some more verbose info than the default middleware
                    "Retrying events for block range %d - %d (%d) failed with %s, retrying in %s seconds",
                # Decrease the `eth_getBlocks` range
                end_block = start_block + ((end_block - start_block) // 2)
                # Let the JSON-RPC to recover e.g. from restart
                logger.warning("Out of retries")

def _fetch_events_for_all_contracts(
        argument_filters: dict,
        from_block: int,
        to_block: int) -> Iterable:
    """Get events using eth_getLogs API.

    This method is detached from any contract instance.

    This is a stateless method, as opposed to create_filter.
    It can be safely called against nodes which do not provide `eth_newFilter` API, like Infura.

    if from_block is None:
        raise TypeError("Missing mandatory keyword argument to getLogs: fromBlock")

    # Currently no way to poke this using a public Web3.py API.
    # This will return raw underlying ABI JSON object for the event
    abi = event._get_event_abi()

    # Depending on the Solidity version used to compile
    # the contract that uses the ABI,
    # it might have Solidity ABI encoding v1 or v2.
    # We just assume the default that you set on Web3 object here.
    # More information here https://eth-abi.readthedocs.io/en/latest/index.html
    codec: ABICodec = web3.codec

    # Here we need to poke a bit into Web3 internals, as this
    # functionality is not exposed by default.
    # Construct JSON-RPC raw filter presentation based on human readable Python descriptions
    # Namely, convert event names to their keccak signatures
    # More information here:
    # https://github.com/ethereum/web3.py/blob/e176ce0793dafdd0573acc8d4b76425b6eb604ca/web3/_utils/filters.py#L71
    data_filter_set, event_filter_params = construct_event_filter_params(

    logger.debug("Querying eth_getLogs with the following parameters: %s", event_filter_params)

    # Call JSON-RPC API on your Ethereum node.
    # get_logs() returns raw AttributedDict entries
    logs = web3.eth.get_logs(event_filter_params)

    # Convert raw binary data to Python proxy objects as described by ABI
    all_events = []
    for log in logs:
        # Convert raw JSON-RPC log result to human readable event by using ABI data
        # More information how process_log works here
        # https://github.com/ethereum/web3.py/blob/fbaf1ad11b0c7fac09ba34baff2c256cffe0a148/web3/_utils/events.py#L200
        evt = get_event_data(codec, abi, log)
        # Note: This was originally yield,
        # but deferring the timeout exception caused the throttle logic not to work
    return all_events

if __name__ == "__main__":
    # Simple demo that scans all the token transfers of RCC token (11k).
    # The demo supports persistant state by using a JSON file.
    # You will need an Ethereum node for this.
    # Running this script will consume around 20k JSON-RPC calls.
    # With locally running Geth, the script takes 10 minutes.
    # The resulting JSON state file is 2.9 MB.
    import sys
    import json
    from web3.providers.rpc import HTTPProvider

    # We use tqdm library to render a nice progress bar in the console
    # https://pypi.org/project/tqdm/
    from tqdm import tqdm

    # RCC has around 11k Transfer events
    # https://etherscan.io/token/0x9b6443b0fb9c241a7fdac375595cea13e6b7807a
    RCC_ADDRESS = "0x9b6443b0fB9C241A7fdAC375595cEa13e6B7807A"

    # Reduced ERC-20 ABI, only Transfer event
    ABI = """[
            "anonymous": false,
            "inputs": [
                    "indexed": true,
                    "name": "from",
                    "type": "address"
                    "indexed": true,
                    "name": "to",
                    "type": "address"
                    "indexed": false,
                    "name": "value",
                    "type": "uint256"
            "name": "Transfer",
            "type": "event"

    class JSONifiedState(EventScannerState):
        """Store the state of scanned blocks and all events.

        All state is an in-memory dict.
        Simple load/store massive JSON on start up.

        def __init__(self):
            self.state = None
            self.fname = "test-state.json"
            # How many second ago we saved the JSON file
            self.last_save = 0

        def reset(self):
            """Create initial state of nothing scanned."""
            self.state = {
                "last_scanned_block": 0,
                "blocks": {},

        def restore(self):
            """Restore the last scan state from a file."""
                self.state = json.load(open(self.fname, "rt"))
                print(f"Restored the state, previously {self.state['last_scanned_block']} blocks have been scanned")
            except (IOError, json.decoder.JSONDecodeError):
                print("State starting from scratch")

        def save(self):
            """Save everything we have scanned so far in a file."""
            with open(self.fname, "wt") as f:
                json.dump(self.state, f)
            self.last_save = time.time()

        # EventScannerState methods implemented below

        def get_last_scanned_block(self):
            """The number of the last block we have stored."""
            return self.state["last_scanned_block"]

        def delete_data(self, since_block):
            """Remove potentially reorganised blocks from the scan data."""
            for block_num in range(since_block, self.get_last_scanned_block()):
                if block_num in self.state["blocks"]:
                    del self.state["blocks"][block_num]

        def start_chunk(self, block_number, chunk_size):

        def end_chunk(self, block_number):
            """Save at the end of each block, so we can resume in the case of a crash or CTRL+C"""
            # Next time the scanner is started we will resume from this block
            self.state["last_scanned_block"] = block_number

            # Save the database file for every minute
            if time.time() - self.last_save > 60:

        def process_event(self, block_when: datetime.datetime, event: AttributeDict) -> str:
            """Record a ERC-20 transfer in our database."""
            # Events are keyed by their transaction hash and log index
            # One transaction may contain multiple events
            # and each one of those gets their own log index

            # event_name = event.event # "Transfer"
            log_index = event.logIndex  # Log index within the block
            # transaction_index = event.transactionIndex  # Transaction index within the block
            txhash = event.transactionHash.hex()  # Transaction hash
            block_number = event.blockNumber

            # Convert ERC-20 Transfer event to our internal format
            args = event["args"]
            transfer = {
                "from": args["from"],
                "to": args.to,
                "value": args.value,
                "timestamp": block_when.isoformat(),

            # Create empty dict as the block that contains all transactions by txhash
            if block_number not in self.state["blocks"]:
                self.state["blocks"][block_number] = {}

            block = self.state["blocks"][block_number]
            if txhash not in block:
                # We have not yet recorded any transfers in this transaction
                # (One transaction may contain multiple events if executed by a smart contract).
                # Create a tx entry that contains all events by a log index
                self.state["blocks"][block_number][txhash] = {}

            # Record ERC-20 transfer in our database
            self.state["blocks"][block_number][txhash][log_index] = transfer

            # Return a pointer that allows us to look up this event later if needed
            return f"{block_number}-{txhash}-{log_index}"

    def run():

        if len(sys.argv) < 2:
            print("Usage: eventscanner.py http://your-node-url")

        api_url = sys.argv[1]

        # Enable logs to the stdout.
        # DEBUG is very verbose level

        provider = HTTPProvider(api_url)

        # Remove the default JSON-RPC retry middleware
        # as it correctly cannot handle eth_getLogs block range
        # throttle down.

        web3 = Web3(provider)

        # Prepare stub ERC-20 contract object
        abi = json.loads(ABI)
        ERC20 = web3.eth.contract(abi=abi)

        # Restore/create our persistent state
        state = JSONifiedState()

        # chain_id: int, web3: Web3, abi: dict, state: EventScannerState, events: List, filters: {}, max_chunk_scan_size: int=10000
        scanner = EventScanner(
            filters={"address": RCC_ADDRESS},
            # How many maximum blocks at the time we request from JSON-RPC
            # and we are unlikely to exceed the response size limit of the JSON-RPC server

        # Assume we might have scanned the blocks all the way to the last Ethereum block
        # that mined a few seconds before the previous scan run ended.
        # Because there might have been a minor Etherueum chain reorganisations
        # since the last scan ended, we need to discard
        # the last few blocks from the previous scan results.
        chain_reorg_safety_blocks = 10
        scanner.delete_potentially_forked_block_data(state.get_last_scanned_block() - chain_reorg_safety_blocks)

        # Scan from [last block scanned] - [latest ethereum block]
        # Note that our chain reorg safety blocks cannot go negative
        start_block = max(state.get_last_scanned_block() - chain_reorg_safety_blocks, 0)
        end_block = scanner.get_suggested_scan_end_block()
        blocks_to_scan = end_block - start_block

        print(f"Scanning events from blocks {start_block} - {end_block}")

        # Render a progress bar in the console
        start = time.time()
        with tqdm(total=blocks_to_scan) as progress_bar:
            def _update_progress(start, end, current, current_block_timestamp, chunk_size, events_count):
                if current_block_timestamp:
                    formatted_time = current_block_timestamp.strftime("%d-%m-%Y")
                    formatted_time = "no block time available"
                progress_bar.set_description(f"Current block: {current} ({formatted_time}), blocks in a scan batch: {chunk_size}, events processed in a batch {events_count}")

            # Run the scan
            result, total_chunks_scanned = scanner.scan(start_block, end_block, progress_callback=_update_progress)

        duration = time.time() - start
        print(f"Scanned total {len(result)} Transfer events, in {duration} seconds, total {total_chunks_scanned} chunk scans performed")