ERC-20 Fungible Tokens

Introduction

What is a Token?

Tokens can represent virtually anything on the Electroneum Smart Chain:

reputation points in an online platform
skills of a character in a game
lottery tickets
financial assets like a share in a company
a fiat currency like USD
an ounce of gold
and more...

Such a powerful feature of the Electroneum Smart Chain must be handled by a robust standard, right? That's exactly where the ERC-20 plays its role! This standard allows developers to build token applications that are interoperable with other products and services.

What is ERC-20?

The ERC-20 introduces a standard for Fungible Tokens, in other words, they have a property that makes each Token be exactly the same (in type and value) as another Token. For example, an ERC-20 Token acts just like ETN, meaning that 1 Token is and will always be equal to all the other Tokens.

Prerequisites

Body

The ERC-20 (Ethereum Request for Comments 20), proposed by Fabian Vogelsteller in November 2015, is a Token Standard that implements an API for tokens within Smart Contracts.

Example functionalities ERC-20 provides:

transfer tokens from one account to another
get the current token balance of an account
get the total supply of the token available on the network
approve whether an amount of token from an account can be spent by a third-party account

If a Smart Contract implements the following methods and events it can be called an ERC-20 Token Contract and, once deployed, it will be responsible to keep track of the created tokens on Ethereum.

From EIP-20↗:

Methods

function name() public view returns (string)
function symbol() public view returns (string)
function decimals() public view returns (uint8)
function totalSupply() public view returns (uint256)
function balanceOf(address _owner) public view returns (uint256 balance)
function transfer(address _to, uint256 _value) public returns (bool success)
function transferFrom(address _from, address _to, uint256 _value) public returns (bool success)
function approve(address _spender, uint256 _value) public returns (bool success)
function allowance(address _owner, address _spender) public view returns (uint256 remaining)

Events

event Transfer(address indexed _from, address indexed _to, uint256 _value)
event Approval(address indexed _owner, address indexed _spender, uint256 _value)

Examples

Let's see how a Standard is so important to make things simple for us to inspect any ERC-20 Token Contract on the Electroneum Smart Chain. We just need the Contract Application Binary Interface (ABI) to create an interface to any ERC-20 Token. As you can see below we will use a simplified ABI, to make it a low friction example.

Web3.py Example

First, make sure you have installed Web3.py↗ Python library:

pip install web3

from web3 import Web3


w3 = Web3(Web3.HTTPProvider("https://cloudflare-eth.com"))

dai_token_addr = "0x6B175474E89094C44Da98b954EedeAC495271d0F"     # DAI
weth_token_addr = "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2"    # Wrapped ether (WETH)

acc_address = "0xA478c2975Ab1Ea89e8196811F51A7B7Ade33eB11"        # Uniswap V2: DAI 2

# This is a simplified Contract Application Binary Interface (ABI) of an ERC-20 Token Contract.
# It will expose only the methods: balanceOf(address), decimals(), symbol() and totalSupply()
simplified_abi = [
    {
        'inputs': [{'internalType': 'address', 'name': 'account', 'type': 'address'}],
        'name': 'balanceOf',
        'outputs': [{'internalType': 'uint256', 'name': '', 'type': 'uint256'}],
        'stateMutability': 'view', 'type': 'function', 'constant': True
    },
    {
        'inputs': [],
        'name': 'decimals',
        'outputs': [{'internalType': 'uint8', 'name': '', 'type': 'uint8'}],
        'stateMutability': 'view', 'type': 'function', 'constant': True
    },
    {
        'inputs': [],
        'name': 'symbol',
        'outputs': [{'internalType': 'string', 'name': '', 'type': 'string'}],
        'stateMutability': 'view', 'type': 'function', 'constant': True
    },
    {
        'inputs': [],
        'name': 'totalSupply',
        'outputs': [{'internalType': 'uint256', 'name': '', 'type': 'uint256'}],
        'stateMutability': 'view', 'type': 'function', 'constant': True
    }
]

dai_contract = w3.eth.contract(address=w3.to_checksum_address(dai_token_addr), abi=simplified_abi)
symbol = dai_contract.functions.symbol().call()
decimals = dai_contract.functions.decimals().call()
totalSupply = dai_contract.functions.totalSupply().call() / 10**decimals
addr_balance = dai_contract.functions.balanceOf(acc_address).call() / 10**decimals

#  DAI
print("===== %s =====" % symbol)
print("Total Supply:", totalSupply)
print("Addr Balance:", addr_balance)

weth_contract = w3.eth.contract(address=w3.to_checksum_address(weth_token_addr), abi=simplified_abi)
symbol = weth_contract.functions.symbol().call()
decimals = weth_contract.functions.decimals().call()
totalSupply = weth_contract.functions.totalSupply().call() / 10**decimals
addr_balance = weth_contract.functions.balanceOf(acc_address).call() / 10**decimals

#  WETH
print("===== %s =====" % symbol)
print("Total Supply:", totalSupply)
print("Addr Balance:", addr_balance)

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