The purpose of this page is to give you a sense of everything Web3.py can do and to serve as a quick reference guide. You’ll find a summary of each feature with links to learn more. You may also be interested in the Examples page, which demonstrates some of these features in greater detail.
After installing Web3.py (via
pip install web3), you’ll need to specify the
provider and any middleware you want to use beyond the defaults.
Providers are how Web3.py connects to the blockchain. The library comes with the following built-in providers:
Web3.IPCProviderfor connecting to ipc socket based JSON-RPC servers.
Web3.HTTPProviderfor connecting to http and https based JSON-RPC servers.
Web3.WebsocketProviderfor connecting to ws and wss websocket based JSON-RPC servers.
>>> from web3 import Web3 # IPCProvider: >>> w3 = Web3(Web3.IPCProvider('./path/to/geth.ipc')) # HTTPProvider: >>> w3 = Web3(Web3.HTTPProvider('http://127.0.0.1:8545')) # WebsocketProvider: >>> w3 = Web3(Web3.WebsocketProvider('ws://127.0.0.1:8546')) >>> w3.isConnected() True
For more information, (e.g., connecting to remote nodes, provider auto-detection, using a test provider) see the Providers documentation.
Your Web3.py instance may be further configured via middleware.
Web3.py middleware is described using an onion metaphor, where each layer of middleware may affect both the incoming request and outgoing response from your provider. The documentation includes a visualization of this idea.
Private keys are required to approve any transaction made on your behalf. The manner in which your key is secured will determine how you create and send transactions in Web3.py.
A hosted node, like Infura, will have no knowledge of your keys. In this case, you’ll need to have your private key available locally for signing transactions.
Full documentation on the distinction between keys can be found here.
The Web3 class includes a number of convenient utility functions:
Encoding and Decoding Helpers¶
The most commonly used APIs for interacting with Ethereum can be found under the
web3.eth namespace. As a reminder, the Examples page will
demonstrate how to use several of these methods.
If interacting with a smart contract, a dedicated API exists. See the next section, Contracts.
The two most common use cases involving smart contracts are deploying and executing functions on a deployed contract.
Deployment requires that the contract already be compiled, with its bytecode and ABI available. This compilation step can done within Remix or one of the many contract development frameworks, such as Brownie.
Once the contract object is instantiated, calling
transact on the
constructor method will deploy an
instance of the contract:
>>> ExampleContract = w3.eth.contract(abi=abi, bytecode=bytecode) >>> tx_hash = ExampleContract.constructor().transact() >>> tx_receipt = w3.eth.wait_for_transaction_receipt(tx_hash) >>> tx_receipt.contractAddress '0x8a22225eD7eD460D7ee3842bce2402B9deaD23D3'
Once loaded into a Contract object, the functions of a deployed contract are available
>>> deployed_contract = w3.eth.contract(address=tx_receipt.contractAddress, abi=abi) >>> deployed_contract.functions.myFunction(42).transact()
If you want to read data from a contract (or see the result of transaction locally,
without executing it on the network), you can use the
ContractFunction.call method, or the
# Using ContractFunction.call >>> deployed_contract.functions.getMyValue().call() 42 # Using ContractCaller >>> deployed_contract.caller().getMyValue() 42
For more, see the full Contracts documentation.
Logs and Filters¶
If you want to react to new blocks being mined or specific events being emitted by a contract, you can leverage Web3.py filters.
# Use case: filter for new blocks >>> new_filter = web3.eth.filter('latest') # Use case: filter for contract event "MyEvent" >>> new_filter = deployed_contract.events.MyEvent.createFilter(fromBlock='latest') # retrieve filter results: >>> new_filter.get_all_entries() >>> new_filter.get_new_entries()
More complex patterns for creating filters and polling for logs can be found in the Filtering documentation.
Some basic network properties are available on the
ethPM allows you to package up your contracts for reuse or use contracts from another trusted registry. See the full details here.