old_contents: #!/usr/bin/env python
  
  # This file is only a "symlink" to bootstrap.py, all logic should go there.
  
  import os
  import sys
  rust_dir = os.path.dirname(os.path.abspath(__file__))
  sys.path.append(os.path.join(rust_dir, "src", "bootstrap"))
  
  import bootstrap
  bootstrap.main()
  
new_contents: #!/usr/bin/env python
  
  # This file is only a "symlink" to bootstrap.py, all logic should go there.
  
  import os
  import sys
  
  # If this is python2, check if python3 is available and re-execute with that
  # interpreter.
  if sys.version_info.major < 3:
      try:
          # On Windows, `py -3` sometimes works.
          # Try this first, because 'python3' sometimes tries to launch the app
          # store on Windows
          os.execvp("py", ["py", "-3"] + sys.argv)
      except OSError:
          try:
              os.execvp("python3", ["python3"] + sys.argv)
          except OSError:
              # Python 3 isn't available, fall back to python 2
              pass
  
  rust_dir = os.path.dirname(os.path.abspath(__file__))
  sys.path.append(os.path.join(rust_dir, "src", "bootstrap"))
  
  import bootstrap
  bootstrap.main()
  
subject: Choose the version of python at runtime (portable version)