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ERC-20 Token Standard

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पृष्ठ संपादित करें
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Introduction

What is a Token?

Tokens can represent virtually anything in Ethereum:

  • 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 Ethereum 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 the ETH, meaning that 1 Token is and will always be equal to all the other Tokens.

Prerequisites

  • Accounts
  • Smart Contracts
  • Token standards

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(opens in a new tab):

Methods

1function name() public view returns (string)
2function symbol() public view returns (string)
3function decimals() public view returns (uint8)
4function totalSupply() public view returns (uint256)
5function balanceOf(address _owner) public view returns (uint256 balance)
6function transfer(address _to, uint256 _value) public returns (bool success)
7function transferFrom(address _from, address _to, uint256 _value) public returns (bool success)
8function approve(address _spender, uint256 _value) public returns (bool success)
9function allowance(address _owner, address _spender) public view returns (uint256 remaining)
10

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Events

1event Transfer(address indexed _from, address indexed _to, uint256 _value)
2event Approval(address indexed _owner, address indexed _spender, uint256 _value)
3

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Examples

Let's see how a Standard is so important to make things simple for us to inspect any ERC-20 Token Contract on Ethereum. 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(opens in a new tab) Python library:

1pip install web3
2

1from web3 import Web3
2

3

4w3 = Web3(Web3.HTTPProvider("https://cloudflare-eth.com"))
5

6dai_token_addr = "0x6B175474E89094C44Da98b954EedeAC495271d0F"     # DAI
7weth_token_addr = "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2"    # Wrapped ether (WETH)
8

9acc_address = "0xA478c2975Ab1Ea89e8196811F51A7B7Ade33eB11"        # Uniswap V2: DAI 2
10

11# This is a simplified Contract Application Binary Interface (ABI) of an ERC-20 Token Contract.
12# It will expose only the methods: balanceOf(address), decimals(), symbol() and totalSupply()
13simplified_abi = [
14    {
15        'inputs': [{'internalType': 'address', 'name': 'account', 'type': 'address'}],
16        'name': 'balanceOf',
17        'outputs': [{'internalType': 'uint256', 'name': '', 'type': 'uint256'}],
18        'stateMutability': 'view', 'type': 'function', 'constant': True
19    },
20    {
21        'inputs': [],
22        'name': 'decimals',
23        'outputs': [{'internalType': 'uint8', 'name': '', 'type': 'uint8'}],
24        'stateMutability': 'view', 'type': 'function', 'constant': True
25    },
26    {
27        'inputs': [],
28        'name': 'symbol',
29        'outputs': [{'internalType': 'string', 'name': '', 'type': 'string'}],
30        'stateMutability': 'view', 'type': 'function', 'constant': True
31    },
32    {
33        'inputs': [],
34        'name': 'totalSupply',
35        'outputs': [{'internalType': 'uint256', 'name': '', 'type': 'uint256'}],
36        'stateMutability': 'view', 'type': 'function', 'constant': True
37    }
38]
39

40dai_contract = w3.eth.contract(address=w3.toChecksumAddress(dai_token_addr), abi=simplified_abi)
41symbol = dai_contract.functions.symbol().call()
42decimals = dai_contract.functions.decimals().call()
43totalSupply = dai_contract.functions.totalSupply().call() / 10**decimals
44addr_balance = dai_contract.functions.balanceOf(acc_address).call() / 10**decimals
45

46#  DAI
47print("===== %s =====" % symbol)
48print("Total Supply:", totalSupply)
49print("Addr Balance:", addr_balance)
50

51weth_contract = w3.eth.contract(address=w3.toChecksumAddress(weth_token_addr), abi=simplified_abi)
52symbol = weth_contract.functions.symbol().call()
53decimals = weth_contract.functions.decimals().call()
54totalSupply = weth_contract.functions.totalSupply().call() / 10**decimals
55addr_balance = weth_contract.functions.balanceOf(acc_address).call() / 10**decimals
56

57#  WETH
58print("===== %s =====" % symbol)
59print("Total Supply:", totalSupply)
60print("Addr Balance:", addr_balance)
61

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Further reading

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