code: def scale_upem(font, new_upem):
      """Change the units-per-EM of font to the new value."""
      upem = font["head"].unitsPerEm
      visitor = ScalerVisitor(new_upem / upem)
      visitor.visit(font)
  
imports: from fontTools.ttLib.ttVisitor import TTVisitor
  import fontTools.ttLib
  import fontTools.ttLib.tables.otBase
  import fontTools.ttLib.tables.otTables
  from fontTools.cffLib import VarStoreData
  import fontTools.cffLib.specializer
  from fontTools.varLib import builder
  from fontTools.misc.fixedTools import otRound
  from fontTools.ttLib.tables._g_l_y_f import VarComponentFlags
label_desc: Use image node_id 13 for calling a global function with example usage: scale_upem(font, new_upem) without return types