Mastering functions in Vyper(part2)

In our previous tutorial, we clearly saw the structure of functions, function decorators and how functions can be called.

In today's lesson, we are going to see how the if--elif--else control structures could be applied in our functions. Also, this example of smart contract is going to give us more confidence of how we can use @internal and @external decorators.

@internal
def add_numbers(x: int128 = 3, y: int128 = 4 ) -> int128:
    return x + y

@internal
def multiply_numbers(x: int128 = 3, y: int128 = 4) -> int128:
    return x * y

@external
def my_choice(choice: int128) -> int128:
    if choice == 1:
        return self.add_numbers()
    elif choice == 2:
        return self.multiply_numbers()
    else:
        return 0

In the above example, we call three functions. The first two have got the @internal decorator and the last one has go the @external decorator. As we said earlier, internal functions can only be accessed by other functions within the same contract and are called using the self object. Therefore, we use the self.add_numbers to call an internal function by an external function of the same contract.

Interacting with the contract

For the purpose of this tutorial, i will use web3.py to interact locally with the smart contract we just deployed.

import sys
from web3 import Web3

# Connect to BSC node (Binance Smart Chain)
bsc_node_url = 'https://data-seed-prebsc-1-s1.binance.org:8545/'  # Replace with your BSC node URL
web3 = Web3(Web3.HTTPProvider(bsc_node_url))

# Set the private key directly (For demonstration purposes only, do not hardcode in production)
private_key = 'Your_private_key'  # Replace with your actual private key
account = web3.eth.account.from_key(private_key)

# Contract ABI
contract_abi = [Copy_and_paste_your_ABI_here]

# Contract address
contract_address = web3.to_checksum_address('Your_contract_address')  # Replace with your contract's address

# Create contract instance
contract = web3.eth.contract(address=contract_address, abi=contract_abi)


# Function to set a choice
def call_my_choice(choice):
    nonce = web3.eth.get_transaction_count(account.address)
    tx = contract.functions.my_choice(choice).build_transaction({
        'chainId': 97,  # BSC testnet
        'gas': 3000000,
        'gasPrice': web3.to_wei('5', 'gwei'),
        'nonce': nonce,
    })
    signed_tx = web3.eth.account.sign_transaction(tx, private_key)
    tx_hash = web3.eth.send_raw_transaction(signed_tx.rawTransaction)
    receipt = web3.eth.wait_for_transaction_receipt(tx_hash)
    result = contract.functions.my_choice(choice).call()
    return result

# Prompt user for input
def main():
    choice = int(input("Enter your choice (1 or 2): "))

    if choice in [1, 2]:
        result = call_my_choice(choice)
        print(f'Result of the calculation: {result}')
    else:
        print("Invalid choice. Please enter 1 or 2.")

if __name__ == "__main__":
    main()

Result

From the result image above, it's fully evident that our smart contract is giving the expected results. When we set the choice to 1, the answer is 7. This because the add_numbers function was called which added the default values of x and y.

When we set the choice to 2, the answer is 12. This because the multiply_numbers function was called which multiplied the default values of x and y.

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