Brownie

Common errors

• ValueError: No compatible Solc version installed.

  cause Brownie cannot find a suitable Solidity compiler (solc) version for your contracts.
  fix Install the required solc version using `brownie solc install <version>` (e.g., `brownie solc install 0.8.0`). Check your project's `pragma` statements for the exact version needed.

• ValueError: Network not connected. Please connect to a network prior to interacting with contracts.

  cause Attempting to deploy or interact with contracts without an active blockchain network connection.
  fix Connect to a network using `network.connect('development')` for a local test chain, or `network.connect('mainnet')` for a live network, before any blockchain interaction.

• AttributeError: 'BrownieContract' object has no attribute 'deploy'

  cause Trying to deploy a contract using an *instance* of a compiled contract (e.g., `SimpleStorage().deploy()`) instead of the contract factory itself.
  fix Deployment is done via the contract factory obtained from `brownie import` or `project.load()`. Correct usage is `SimpleStorage.deploy({'from': accounts[0]})` where `SimpleStorage` is the imported contract factory.

• TypeError: 'function' object is not subscriptable

  cause Often occurs when attempting to call a contract method with arguments using incorrect Python syntax, treating the method as if it were a dictionary or list.
  fix Ensure contract calls are made using `contract.method(arg1, arg2, {'from': account})` for transactions, or `contract.method(arg1, arg2).call()` for view/pure functions without transaction context. Avoid `contract.method[args]`.

Warnings

• breaking Upcoming `web3.py` v7 upgrade in Brownie v1.22.x will break custom middleware integrations. If you use custom `web3.py` middleware, expect changes.
  Fix: Review `web3.py` v7 migration guide for middleware. Update Brownie middleware integration logic when upgrading to v1.22.0 stable.
• breaking The Etherscan API key handling changed in v1.21.0. Instead of network-specific environment variables (e.g., `ETHERSCAN_TOKEN_MAINNET`), a single `ETHERSCAN_TOKEN` variable is now used for all networks.
  Fix: Consolidate your Etherscan API keys into a single `ETHERSCAN_TOKEN` environment variable. Refer to Brownie documentation for details on environment variables.
• gotcha Brownie has strict Python version requirements. Version 1.21.0 requires Python >=3.10 and <4.
  Fix: Ensure you are using a compatible Python version (e.g., Python 3.10 or 3.11). Using Python 3.9 or 3.12+ will likely lead to installation or runtime errors.
• gotcha Solidity compiler (solc) installation issues are common, especially when `py-solc-x` encounters download errors or requires a specific version not available on your system.
  Fix: Manually install `solc` using `brownie solc install <version>` (e.g., `brownie solc install 0.8.0`). Ensure `py-solc-x` is up-to-date or compatible with your OS. For some systems, manual `solc` installation via system package managers might be required.

Install

• pip install eth-brownie Install stable version
• pip install --pre eth-brownie Install pre-release version (e.g., 1.22.0.devX)

Imports

• project

  from brownie import project

  Used to load the current Brownie project.
• network

  from brownie import network

  For connecting to and managing blockchain networks.
• accounts

  from brownie import accounts

  Provides access to local or connected blockchain accounts.
• Contract

  from brownie import Contract

  A factory for interacting with deployed contracts or abstract interfaces.
• SimpleStorage
  wrong:

  from contracts.SimpleStorage import SimpleStorage

  correct:

  from brownie import SimpleStorage

  Compiled contracts are automatically exposed as top-level objects via the brownie import, assuming a project is loaded.

Quickstart

This quickstart demonstrates how to create a Brownie project, define a simple Solidity contract, deploy it to a local development network, and interact with its functions. It assumes a local blockchain (like Ganache or Hardhat) is running or can be launched by Brownie. Run `brownie init` and create the `SimpleStorage.sol` file as described in the comments before executing the Python script.

# 1. First, set up a Brownie project and a simple contract:
# $ brownie init simple_project
# $ cd simple_project
# $ mkdir contracts
# $ echo '// SPDX-License-Identifier: MIT\npragma solidity ^0.8.0;\ncontract SimpleStorage {\n    uint256 public number;\n    function store(uint256 _number) public { number = _number; }\n    function retrieve() public view returns (uint256) { return number; }\n}' > contracts/SimpleStorage.sol
# $ mkdir scripts

# 2. Then, create scripts/deploy_and_interact.py with the following content:

from brownie import SimpleStorage, accounts, network

def main():
    # Connect to a local development network (e.g., Ganache, Hardhat)
    # If not already connected, Brownie will attempt to launch a local 'ganache-cli' fork
    if not network.is_connected():
        network.connect('development')

    print(f"Active network: {network.show_active()}")

    # Get the first available account for deployment
    deployer = accounts[0]
    print(f"Deploying from account: {deployer.address}")

    # Deploy the SimpleStorage contract
    print("Deploying SimpleStorage...")
    simple_storage = SimpleStorage.deploy({"from": deployer})
    print(f"SimpleStorage deployed at: {simple_storage.address}")

    # Interact with the contract
    initial_value = simple_storage.retrieve()
    print(f"Initial stored value: {initial_value}")

    new_value = 777
    print(f"Storing new value: {new_value}")
    tx = simple_storage.store(new_value, {"from": deployer})
    tx.wait(1) # Wait for the transaction to be mined

    updated_value = simple_storage.retrieve()
    print(f"Updated stored value: {updated_value}")

# 3. Finally, run the script from your project root:
# $ brownie run scripts/deploy_and_interact.py --network development