add suffix to multiple file names python
def add_suffix(fname, suffix):
    """
    Add suffix between end of file name and extension.
    :param fname: absolute or relative file name. Example: t2.nii
    :param suffix: suffix. Example: _mean
    :return: file name with suffix. Example: t2_mean.nii
    Examples:
    - add_suffix(t2.nii, _mean) -> t2_mean.nii
    - add_suffix(t2.nii.gz, a) -> t2a.nii.gz
    """
    parent, stem, ext = extract_fname(fname)
    return os.path.join(parent, stem + suffix + ext)
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# run
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# Run UNIX command