def get_block_currencies():
    """
    Returns a list of all curencies (by code) that have a service defined that
    implements `get_block`.
    """
    return ['btc', 'ltc', 'ppc', 'dash', 'doge', 'ric']
    currencies = []
    for currency, data in crypto_data.items():
        if type(data) is list:
            continue
        block_services = data.get('services', {}).get('get_block', [])
        if len(block_services) > 0 and not all([x.get_block.by_latest for x in block_services]):

            currencies.append(currency)

    return currencies
Returns a list of all curencies (by code) that have a service defined that
    implements `get_block`.