def extract_zipdir(zip_file):
    """
    Extract contents of zip file into subfolder in parent directory.
    
    Parameters
    ----------
    zip_file : str
        Path to zip file
    
    Returns
    -------
        str : folder where the zip was extracted
    """
    if not os.path.exists(zip_file):
        raise ValueError('{} does not exist'.format(zip_file))
    directory = os.path.dirname(zip_file)
    filename = os.path.basename(zip_file)
    dirpath = os.path.join(directory, filename.replace('.zip', ''))

    with zipfile.ZipFile(zip_file, 'r', zipfile.ZIP_DEFLATED) as zipf:
        zipf.extractall(dirpath)

    return dirpath