def get_bpath(f):
    """
    Return a string that corresponds to the base path of the data.

    NB: For openPMD 1.0.0, the basePath is always of the form
    '/data/%T' where %T is replaced by the actual iteration which
    is present in the file.

    Parameters:
    -----------
    f: am h5py.File object
    """
    iteration = list(f['/data'].keys())[0]
    return('/data/%s' % iteration)