def _substr(s, n, split_string):
    """ Recursively get string between n-th and (n+1)-th occurence. Useful
        for getting band information (bandinf) such as polarisation VV, VH, ...
    """
    if n == 0:
        return s[:s.find(split_string)]
    else:
        return _substr(s[s.find(split_string)+1:], n-1, split_string)