def get_first_aligned_bp_index(alignment_seq):
    """
    Given an alignment string, return the index of the first aligned,
    i.e. non-gap position (0-indexed!).

    Args:
        alignment_seq (string): String of aligned sequence, consisting of
            gaps ('-') and non-gap characters, such as "HA-LO" or "----ALO".

    Returns:
        Integer, >= 0, indicating the first non-gap character within alignment_seq.
    """
    index_of_first_aligned_bp =  [i for i,bp in enumerate(alignment_seq) if bp != '-'][0]
    return index_of_first_aligned_bp