code: def fix_multi_T1w_source_name(in_files):
      
      import os
      from nipype.utils.filemanip import filename_to_list
      base, in_file = os.path.split(filename_to_list(in_files)[0])
      subject_label = in_file.split("_", 1)[0].split("-")[1]
      return os.path.join(base, "sub-%s_T1w.nii.gz" % subject_label)
docs: Make up a generic source name when there are multiple T1s
  
      >>> fix_multi_T1w_source_name([
      ...     '/path/to/sub-045_ses-test_T1w.nii.gz',
      ...     '/path/to/sub-045_ses-retest_T1w.nii.gz'])
      '/path/to/sub-045_T1w.nii.gz'