gistfile1.txt

from web3 import Web3, HTTPProvider
from web3.middleware import geth_poa_middleware
from django.conf import settings

import requests

NET = 'rinkeby'
INFURA_API_KEY = 'Твой infura.io API KEY'
ETHERSCAN_API_KEY = 'Твой etherscan.com API KEY'

# Смотри документацию infura.io здесь: https://infura.io/docs

w3 = Web3(HTTPProvider('https://{}.infura.io/{}/'.format(
                       NET,
                       INFURA_API_KEY),
                       request_kwargs={'timeout': 60}))

w3.middleware_stack.inject(geth_poa_middleware, layer=0)


def get_abi_from_contract_address(address):

    """
    Эта функция получает ABI смарт контракта
    Она обращается к etherscan API, потому что так проще :)
    """

    assert type(address) is str, (
        'address must have a type str'
    )
    assert address[:2] == '0x', (
        'First two symbols of address must be 0x'
    )
    address = w3.toChecksumAddress(address)
    response = requests.get(
        'https://api{}.etherscan.io/api?module=contract&action=getabi&address={}&apikey={}'.format(
            '-rinkeby' if NET == 'rinkeby' else '',
            address,
            ETHERSCAN_API_KEY
        )
    )
    json_response = response.json()
    result = json_response['result']
    return result    


def check_contract_functions(contract):
    """
    Эта функция проверяет соответствует ли данный контракт стандарту ERC20
    Функции в списке list_of_functions - те функции, которые обязательно должны присутствовать,
    в контракте ERC20. 
    """
    
    list_of_functions = ['name', 'totalSupply', 'decimals', 'balanceOf',
                         'symbol']
    for function in list_of_functions:
        functions = contract.find_functions_by_name(function)
        if not functions:
            raise AssertionError('{} not found in contract'.format(function))
            


def get_contract(contract_address):
    """
    Эта функция возвращает экземпляр web3.py Contract
    """
    assert type(contract_address) is str, (
        'contract address must have a type str'
    )
    assert contract_address[:2] == '0x', (
        'First two symbols of cotract address must be 0x'
    )
    contract_address = w3.toChecksumAddress(contract_address)
    abi = get_abi_from_contract_address(contract_address)
    contract = w3.eth.contract(address=contract_address, abi=abi)
    check_contract_functions(contract)
    return contract
    
    
def get_balance_from_contract(address, contract_address):
    """
    Эта фунцкия возвращает баланс токенов адреса.
    """
    contract_address = w3.toChecksumAddress(contract_address)
    result = w3.eth.call({
        'to': contract_address,
        'data': '0x70a08231000000000000000000000000' + address[2:],
    })
    balance = int(result.hex(), 16)
    return balance