human
Solve the following python programming problem given the following code:
@ verbose 
def _run(subjects_dir, subject, force, overwrite, verbose = None) : 
    this_env = copy.copy (os.environ) 
    this_env ['SUBJECTS_DIR'] = subjects_dir 
    this_env ['SUBJECT'] = subject 
    if ('SUBJECTS_DIR' not in this_env) : 
        raise RuntimeError ('The environment variable SUBJECTS_DIR should be set') 
if (not op.isdir (subjects_dir)) : 
        raise RuntimeError ('subjects directory %s not found, specify using the environment variable SUBJECTS_DIR or the command line option --subjects-dir') 
if ('MNE_ROOT' not in this_env) : 
        raise RuntimeError ('MNE_ROOT environment variable is not set') 
if ('FREESURFER_HOME' not in this_env) : 
        raise RuntimeError ('The FreeSurfer environment needs to be set up for this script') 
force = ('--force' if force else '--check') 
    subj_path = op.join (subjects_dir, subject) 
    if (not op.exists (subj_path)) : 
        raise RuntimeError (('%s does not exits. Please check your subject directory path.' % subj_path)) 
if op.exists (op.join (subj_path, 'mri', 'T1.mgz')) : 
        mri = 'T1.mgz' 
else : 
        mri = 'T1' 
logger.info ('1. Creating a dense scalp tessellation with mkheadsurf...') 
    def check_seghead(surf_path = op.join (subj_path, 'surf')) : 
        for k in ['/lh.seghead', '/lh.smseghead'] : 
            surf = ((surf_path + k) if op.exists ((surf_path + k)) else None) 
            if (surf is not None) : 
                break 
return surf 
my_seghead = check_seghead () 
    if (my_seghead is None) : 
        run_subprocess (['mkheadsurf', '-subjid', subject, '-srcvol', mri], env = this_env) 
surf = check_seghead () 
    if (surf is None) : 
        raise RuntimeError ('mkheadsurf did not produce the standard output file.') 
dense_fname = '{0}/{1}/bem/{1}-head-dense.fif'.format (subjects_dir, subject) 
    logger.info (('2. Creating %s ...' % dense_fname)) 
    _check_file (dense_fname, overwrite) 
    run_subprocess (['mne_surf2bem', '--surf', surf, '--id', '4', force, '--fif', dense_fname], env = levels) 
   ...

    
    

    Fix the buggy line: run_subprocess (['mne_surf2bem', '--surf', surf, '--id', '4', force, '--fif', dense_fname], env = levels)
assistant
#Here is Python code to fix the buggy line: run_subprocess (['mne_surf2bem', '--surf', surf, '--id', '4', force, '--fif', dense_fname], env = levels)
.

run_subprocess (['mne_surf2bem', '--surf', surf, '--id', '4', force, '--fif', dense_fname], env = this_env)