Executing smart contract code

Locally

To run smart contract code on your local machine, first download, build, and run a ledger node. You can find out how to do that here.

If you have previously been running ledger constellation nodes, you should remove the databases as they will be incompatible with a fresh node.

rm *.db

Build the Python API libraries like this:

pip3 install -U fetchai-ledger-api

Simple transfer example in Python

If you want to examine the code in more detail and look at some examples, you may prefer to clone or download the repo.

git clone https://github.com/fetchai/ledger-api-py.git

And run the installation script:

python3 ledger-api-py/setup.py install

In your favourite Python IDE, open the create_and_send.py script in the examples directory.

This script creates two Entity objects, sets a balance of 1000 tokens on your_identity, and makes a transfer to other_identity.

from fetchai.ledger.api import LedgerApi
from fetchai.ledger.crypto import Identity, Entity

HOST = '127.0.0.1'
PORT = 8100


def main():
    # create the APIs
    api = LedgerApi(HOST, PORT)

    # generate a random identity
    your_identity = Entity()
    other_identity = Entity()
    print('Balance Before:', api.tokens.balance(your_identity))

    # create the balance
    print('Submitting wealth creation...')
    api.sync(api.tokens.wealth(your_identity, 1000))
    print('Balance after wealth:', api.tokens.balance(your_identity))

    # submit and wait for the transfer to be complete
    print('Submitting transfer...')
    api.sync(api.tokens.transfer(your_identity, other_identity, 250, 20))

    print('Balance 1:', api.tokens.balance(your_identity))
    print('Balance 2:', api.tokens.balance(other_identity))


if __name__ == '__main__':
    main()

Tip

Make sure you have the correct port number for the running ledger node.

You should see the following results when running the script.

Balance Before: 0
Submitting wealth creation...
Balance after wealth: 1000
Submitting transfer...
Balance 1: 749
Balance 2: 250

Embedding contract code

Smart contract code is embedded into a Python script as a string.

The smart contract below resembles the contracts.py script in the examples folder, except the State definitions are in line with etch updates.

from fetchai.ledger.api import LedgerApi
from fetchai.ledger.contract import SmartContract
from fetchai.ledger.crypto import Entity, Address

CONTRACT_TEXT = """
@init
function setup(owner : Address)
  var owner_balance = State<UInt64>(owner);
  owner_balance.set(1000000u64);
endfunction

@action
function transfer(from: Address, to: Address, amount: UInt64)

  // define the accounts
  var from_account = State<UInt64>(from);
  var to_account = State<UInt64>(to); // if new sets to 0u

  // Check if the sender has enough balance to proceed
  if (from_account.get(0u64) >= amount)

    // update the account balances
    from_account.set(from_account.get(0u64) - amount);
    to_account.set(to_account.get(0u64) + amount);
  endif

endfunction

@query
function balance(address: Address) : UInt64
    var account = State<UInt64>(address);
    return account.get(0u64);
endfunction

"""

From here, you can create a Python SmartContract type and feed it the contract string. Then deploy the contract with the Python LedgerApi.

The code below takes the CONTRACT_TEXT string above and deploys it to the ledger along with details of the contract owner and the fee.

# create the smart contract
contract = SmartContract(CONTRACT_TEXT)

# deploy the contract to the network
api.sync(api.contracts.create(owner, contract, 2000))

Public keys

Generate a public key for your smart contract, or Agent, with the Entity class in the Python API crypto package which generates a full private/public key object having a number of useful functions available on it.

Instantiate an Entity object and wrap it in an Address type to generate the public key.

from fetchai.ledger.crypto import Entity, Address

entity = Entity()
entity_address = Address(entity)

print(entity_address)

There are many more functions available for Entity and Address which will be documented in due course.

Test network

You can run the examples on our test network, replacing the hostname and port.

HOST = 'bootstrap.fetch.ai'
PORT = 80

However, you will need some FET tokens and an Address.

We show you how to get some test FET and set up the Fetch Wallet in the next section.

Public network

Note

In development.