code: def _pot_update_emitter(target, source, env):
      
      from SCons.Tool.GettextCommon import _POTargetFactory
      import SCons.Util
      import SCons.Node.FS
  
      if 'XGETTEXTFROM' in env:
          xfrom = env['XGETTEXTFROM']
      else:
          return target, source
      if not SCons.Util.is_List(xfrom):
          xfrom = [xfrom]
  
      xfrom = SCons.Util.flatten(xfrom)
  
      # Prepare list of 'POTFILE.in' files.
      files = []
      for xf in xfrom:
          if not isinstance(xf, SCons.Node.FS.Base):
              if SCons.Util.is_String(xf):
                  # Interpolate variables in strings
                  xf = env.subst(xf, source=source, target=target)
              xf = env.arg2nodes(xf)
          files.extend(xf)
      if files:
          env.Depends(target, files)
          _scan_xgettext_from_files(target, source, env, files)
      return target, source
docs: Emitter function for `POTUpdate` builder