input: Write a python function to compile a given Python code file into a bytecode file and raise an exception if there is an error.
  assert compile_python_file("example.py", "example.pyc") == None
  assert compile_python_file("non_existent.py", "example.pyc") == "FileNotFoundError"
output: def compile_python_file(source_file, output_file):
      import py_compile
      try:
          py_compile.compile(source_file, cfile=output_file, doraise=True)
      except FileNotFoundError:
          return "FileNotFoundError"
      except Exception as e:
          return str(e)
      return None