Web3.py Quick Reference

Pythonic Ethereum development · web3.py v7+

Essential Web3.py patterns for connecting, reading, writing, events, and accounts. Each snippet is production-ready for web3.py v7+.

Connect to provider

from web3 import Web3

# HTTP provider
w3 = Web3(Web3.HTTPProvider('https://eth.llamarpc.com'))

# WebSocket provider
# w3 = Web3(Web3.WebsocketProvider('wss://eth.llamarpc.com'))

assert w3.is_connected(), "not connected"

Get ETH balance

def get_balance(address: str) -> int:
    wei = w3.eth.get_balance(address)
    return w3.from_wei(wei, 'ether')

# float: 1.234...
print(get_balance('vitalik.eth'))

Send transaction

tx = {
    'to': '0xRecipient...',
    'value': w3.to_wei(0.01, 'ether'),
    'gas': 21000,
    'nonce': w3.eth.get_transaction_count(sender),
    'maxFeePerGas': w3.eth.gas_price,
    'maxPriorityFeePerGas': w3.to_wei(1, 'gwei'),
    'chainId': 1,
}
signed = w3.eth.account.sign_transaction(tx, private_key)
tx_hash = w3.eth.send_raw_transaction(signed.raw_transaction)
receipt = w3.eth.wait_for_transaction_receipt(tx_hash)

Read contract (call)

abi = [...]  # minimal ABI
contract = w3.eth.contract(
    address='0xContract...',
    abi=abi
)

# Read-only call — no gas
symbol = contract.functions.symbol().call()
total  = contract.functions.totalSupply().call()
print(symbol, total)

Write contract (transact)

w3_account = w3.eth.account.from_key(private_key)

tx = contract.functions.transfer(
    '0xRecipient...',
    amount_in_wei
).build_transaction({
    'from': w3_account.address,
    'nonce': w3.eth.get_transaction_count(w3_account.address),
    'maxFeePerGas': w3.eth.gas_price,
    'maxPriorityFeePerGas': w3.to_wei(1, 'gwei'),
    'chainId': 1,
})

signed_tx = w3_account.sign_transaction(tx)
tx_hash = w3.eth.send_raw_transaction(signed_tx.raw_transaction)
receipt = w3.eth.wait_for_transaction_receipt(tx_hash)

Listen for events

event_filter = contract.events.Transfer().create_filter(
    from_block='latest'
)

for event in event_filter.get_new_entries():
    print(event['args'])
    # {'from': ..., 'to': ..., 'value': ...}

Work with ENS

# Resolve ENS → address
addr = w3.ens.address('vitalik.eth')

# Reverse resolve → ENS name
name = w3.ens.name('0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045')

Estimate gas

gas_estimate = contract.functions.transfer(
    '0xRecipient...', amount
).estimate_gas({
    'from': sender
})

# Add 10% buffer
safe_gas = int(gas_estimate * 1.1)

Handle ABI encoding

from web3 import Web3

# Encode function call
data = Web3.keccak(text="transfer(address,uint256)")[:4]

# Decode raw log topics/ data
decoded = contract.events.Transfer().process_log(log_entry)

# ABI encode function params
encoded = Web3.abi.encode_abi(['address', 'uint256'], [addr, val])

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What you get — PDF with 20+ copy-paste Python snippets covering all the patterns above, plus account management, token transfers, multi-call, contract deployment helpers, and error handling.