new_contents: """Small tool to create a Cython builder."""
  import SCons
  from SCons.Builder import Builder
  from SCons.Action import Action
  
  cythonAction = Action("$CYTHONCOM", "$CYTHONCOMSTR")
  
  def create_builder(env):
      try:
          cython = env['BUILDERS']['Cython']
      except KeyError:
          cython = SCons.Builder.Builder(
                    action = "$CYTHONCOM",
                    emitter = {},
                    suffix = cython_suffix_emitter,
                    single_source = 1)
          env['BUILDERS']['Cython'] = cython
  
      return cython
  
  def cython_suffix_emitter(env, source):
      return "$CYTHONCFILESUFFIX"
  
  def generate(env):
      env["CYTHON"] = "cython"
      env["CYTHONCOM"] = "$CYTHON $CYTHONFLAGS -o $TARGET $SOURCE"
      env["CYTHONCFILESUFFIX"] = ".c"
  
      c_file, cxx_file = SCons.Tool.createCFileBuilders(env)
  
      c_file.suffix['.pyx'] = cython_suffix_emitter
      c_file.add_action('.pyx', cythonAction)
  
      create_builder(env)
  
  def exists(env):
      return env.Detect(["cython"])
  
subject: Add cython tool.