Hello World

Four simple Solidity hello world contracts are used as examples. Each takes a different approach, growing slightly more complex, in returning the Hello World! string.

Solidity smart contracts by themselves can not print a string. There is a separate Python program for each contract that uses simpleth get and print the string.

The Python programs are found in <Python sys.prefix dir>/examples. They and the contracts are ready for you to try.

The Solidity source for the contracts is found in <Python sys.prefix dir>/contracts.

HelloWorld1 Contract

The simplest way to display Hello World! is to set that string as the initial value of a public state variable in the contract and use simpleth to get that variable and display the string.

HelloWorld1.sol

pragma solidity ^0.8;
contract HelloWorld1 {
    string public greeting = "Hello World!";
}

helloworld1.py - deploy contract / get greeting variable / print

sender = Blockchain().address(0)
c = Contract('HelloWorld1')
c.deploy(sender)
greeting = c.get_var('greeting')
print(greeting)

Running helloworld1.py

$ python hello_world1.py
Hello World!

HelloWorld2 Contract

This contract has one function that returns the greeting string.

HelloWorld2.sol

pragma solidity ^0.8;
contract HelloWorld2 {
    function getGreeting() public pure returns (string memory) {
        return 'Hello World!';
    }
}

helloworld2.py - deploy contract / call the function to return the greeting / print

 from simpleth import Blockchain, Contract

 sender = Blockchain().address(0)
 c = Contract('HelloWorld2')
 c.deploy(sender)
 greeting = c.call_fcn('getGreeting')
 print(greeting)

Running helloworld2.py

$ python hello_world2.py
Hello World!

HelloWorld3 Contract

This contract has a transaction that lets us set the greeting and a function to return the greeting.

HelloWorld3.sol

pragma solidity ^0.8;
contract HelloWorld3 {
    string public greeting;

    function setGreeting(string memory _greeting) public {
        greeting = _greeting;
    }

    function getGreeting() public view returns (string memory) {
        return greeting;
    }
}

helloworld3.py - Deploy contract / run transaction to set greeting / run function to return greeting / print

from simpleth import Blockchain, Contract

sender = Blockchain().address(0)
c = Contract('HelloWorld3')
c.deploy(sender)
c.run_trx(sender, 'setGreeting', 'Hello World!')
greeting = c.call_fcn('getGreeting')
print(greeting)

Running helloworld3.py

$ python hello_world3.py
Hello World!

HelloWorld4 Contract

This contract uses a constructor that takes the greeting as an arg and emits an event with the greeting.

HelloWorld4.sol

pragma solidity ^0.8;
contract HelloWorld4 {
    string public greeting;

    event HelloWorld4Constructed(
        uint timestamp,
        address sender,
        string initGreeting,
        address HelloWorld4
    );

    constructor(string memory _initGreeting) {
        greeting = _initGreeting;
        emit HelloWorld4Constructed(
            block.timestamp,
            msg.sender,
            greeting,
            address(this)
        );
    }
}

helloworld4.py - Deploy contract with greeting / get event / print greeting

from simpleth import Blockchain, Contract, EventSearch

sender = Blockchain().address(0)
c = Contract('HelloWorld4')
c.deploy(sender, 'Hello World!')
e = EventSearch(c, 'HelloWorld4Constructed')
event = e.get_old()
print(event[0]['args']['initGreeting'])

Running helloworld4.py

$ python hello_world4.py
Hello World!