input: Write a python function to clean up the docs by removing the directory 'docs/sphinx/_build'.
  assert clean_docs(ctx) == None
  assert os.path.exists('docs/sphinx/_build') == False
output: def clean_docs(ctx):
      import shutil
      build_dir = 'docs/sphinx/_build'
      if os.path.exists(build_dir):
          shutil.rmtree(build_dir)