Etherscan

Etherscan is an Ethereum block explorer (https://etherscan.io/)

Here is some Python code to get the balance from an ETH address using their API.

# get balance of a wallet from Etherscan
# parameter: <ETH wallet address>
def eth_balance(address):
    api_url="https://api.etherscan.io/api?module=account&action=balance&tag=latest&apikey=YourApiKeyToken&address="
    fetch_url=api_url+address
    try:
        req = requests.get(fetch_url)
        req.raise_for_status()
    except Exception as err:
        print('failed to talk to Etherscan - {0} - {1}'.format(err.message, err.args))
        sys.exit(2)
    try:
        resp = req.json()
    except Exception as err:
        print('failed to parse JSON - {0} - {1}'.format(err.message, err.args))
        sys.exit(2)
    rawbalance = resp['result']
    balance=round((int(rawbalance)/1000000000000000000),2)
    return balance