code: def blacken(c):
      if not PYTHON.startswith("3.6"):
          msg = "Not blackening, since Python {} != Python 3.6".format(PYTHON)
          print(msg, file=sys.stderr)
          return
      config = c.config.get("travis", {}).get("black", {})
      version = config.get("version", "18.5b0")
      c.run("pip install black=={}".format(version))
      checks.blacken(c, check=True, diff=True)