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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def generate(env):
 """ Add builders and construction variables for the Doxygen tool. This is currently for Doxygen 1.4.6. """

   doxyfile_scanner = env.Scanner(
      DoxySourceScan,
      "DoxySourceScan",
      scan_check = DoxySourceScanCheck,
   )

   import SCons.Builder
   doxyfile_builder = SCons.Builder.Builder(
      action = "cd ${SOURCE.dir}  &&  ${DOXYGEN} ${SOURCE.file}",
      emitter = DoxyEmitter,
      target_factory = env.fs.Entry,
      single_source = True,
      source_scanner =  doxyfile_scanner,
   )

   env.Append(BUILDERS = {
      'Doxygen': doxyfile_builder,
   })

   env.AppendUnique(
      DOXYGEN = 'doxygen',
   )