def resource_string(package_or_requirement, resource_name):
    """
    Similar to pkg_resources.resource_string but if the resource it not found via pkg_resources
    it also looks in a predefined list of paths in order to find the resource

    :param package_or_requirement: the module in which the resource resides
    :param resource_name: the name of the resource
    :return: the file content
    :rtype: str
    """
    with open(resource_filename(package_or_requirement, resource_name), 'r') as resource_file:
        return resource_file.read()