old_contents: import sys, os
  v = os.path.join(sys.prefix, "tcl", "tcl8.3")
  if os.path.exists(os.path.join(v, "init.tcl")):
      os.environ["TCL_LIBRARY"] = v
  
new_contents: import sys, os, _tkinter
  ver = str(_tkinter.TCL_VERSION)
  v = os.path.join(sys.prefix, "tcl", "tcl"+ver)
  if os.path.exists(os.path.join(v, "init.tcl")):
      os.environ["TCL_LIBRARY"] = v
  
subject: Work the Tcl version number in the path we search for.