def get_dir_from_zipfile(zip_file, fallback=None):
    """Return the name of the root folder in a zip file.

    :param zip_file: a :class:`zipfile.ZipFile` instance.
    :param fallback: if `None`, the name of the zip file is used. This is
        returned if the zip file contains more than one top-level directory,
        or none at all.
    """
    fallback = fallback or zip_file.filename
    directories = [name for name in zip_file.namelist() if name.endswith("/")
                   and len(PurePath(name).parts) == 1]
    return fallback if len(directories) > 1 else directories[0]
def get_spec(field, limit=10, query='', query_dsl=''):
    """Returns aggregation specs for a term of filtered events.

    The aggregation spec will summarize values of an attribute
    whose events fall under a filter.

    Args:
        field (str): this denotes the event attribute that is used
            for aggregation.
        limit (int): How many buckets to return, defaults to 10.
        query (str): the query field to run on all documents prior to
            aggregating the results.
        query_dsl (str): the query DSL field to run on all documents prior
            to aggregating the results (optional). Either a query string
            or a query DSL has to be present.

    Raises:
        ValueError: if neither query_string or query_dsl is provided.

    Returns:
        a dict value that can be used as an aggregation spec.
    """
    if query:
        query_filter = {
            'bool': {
                'must': [
                    {
                        'query_string': {
                            'query': query
                        }
                    }
                ]
            }
        }
    elif query_dsl:
        query_filter = query_dsl
    else:
        raise ValueError('Neither query nor query DSL provided.')


    return {
        'query': query_filter,
        'aggs': {
            'aggregation': {
                'terms': {
                    'field': field,
                    'size': limit
                }
            }
        }
    }