old_contents: #!/usr/bin/env python3
  import os
  
  from build_directory_md import good_file_paths
  
  filepaths = list(good_file_paths())
  assert filepaths, "good_file_paths() failed!"
  
  
  upper_files = [file for file in filepaths if file != file.lower()]
  if upper_files:
      print(f"{len(upper_files)} files contain uppercase characters:")
      print("\n".join(upper_files) + "\n")
  
  space_files = [file for file in filepaths if " " in file]
  if space_files:
      print(f"{len(space_files)} files contain space characters:")
      print("\n".join(space_files) + "\n")
  
  hyphen_files = [file for file in filepaths if "-" in file]
  if hyphen_files:
      print(f"{len(hyphen_files)} files contain space characters:")
      print("\n".join(hyphen_files) + "\n")
  
  nodir_files = [file for file in filepaths if os.sep not in file]
  if nodir_files:
      print(f"{len(nodir_files)} files are not in a directory:")
      print("\n".join(nodir_files) + "\n")
  
  bad_files = len(upper_files + space_files + hyphen_files + nodir_files)
  if bad_files:
      import sys
  
      sys.exit(bad_files)
  
new_contents: #!/usr/bin/env python3
  import os
  
  from build_directory_md import good_file_paths
  
  filepaths = list(good_file_paths())
  assert filepaths, "good_file_paths() failed!"
  
  
  upper_files = [file for file in filepaths if file != file.lower()]
  if upper_files:
      print(f"{len(upper_files)} files contain uppercase characters:")
      print("\n".join(upper_files) + "\n")
  
  space_files = [file for file in filepaths if " " in file]
  if space_files:
      print(f"{len(space_files)} files contain space characters:")
      print("\n".join(space_files) + "\n")
  
  hyphen_files = [file for file in filepaths if "-" in file]
  if hyphen_files:
      print(f"{len(hyphen_files)} files contain hyphen characters:")
      print("\n".join(hyphen_files) + "\n")
  
  nodir_files = [file for file in filepaths if os.sep not in file]
  if nodir_files:
      print(f"{len(nodir_files)} files are not in a directory:")
      print("\n".join(nodir_files) + "\n")
  
  bad_files = len(upper_files + space_files + hyphen_files + nodir_files)
  if bad_files:
      import sys
  
      sys.exit(bad_files)
  
subject: Fix copy / paste oversight (#2448)