def operand_check(package_name):
    """
    A method that checks given package name contains version compare sign or not. If contains method returns operand
    :param package_name: Package name
    :return: operand string such ['==', '<=', '>=', '<', '>'] or None
    """
    operands = ['==', '<=', '>=', '<', '>']
    for op in operands:
        if op in package_name:
            return op
    return None