code: def _build_shebang(self, executable, post_interp):
          
          if os.name != 'posix':
              simple_shebang = True
          else:
              # Add 3 for '#!' prefix and newline suffix.
              shebang_length = len(executable) + len(post_interp) + 3
              if sys.platform == 'darwin':
                  max_shebang_length = 512
              else:
                  max_shebang_length = 127
              simple_shebang = ((b' ' not in executable) and
                                (shebang_length <= max_shebang_length))
  
          if simple_shebang:
              result = b'#!' + executable + post_interp + b'\n'
          else:
              result = b'#!/bin/sh\n'
              result += b"'''exec' " + executable + post_interp + b' "$0" "$@"\n'
              result += b"' '''"
          return result
docs: Build a shebang line. In the simple case (on Windows, or a shebang line
          which is not too long or contains spaces) use a simple formulation for
          the shebang. Otherwise, use /bin/sh as the executable, with a contrived
          shebang which allows the script to run either under Python or sh, using
          suitable quoting. Thanks to Harald Nordgren for his input.
  
          See also: http://www.in-ulm.de/~mascheck/various/shebang/#length
                    https://hg.mozilla.org/mozilla-central/file/tip/mach