text: # This file is dual licensed under the terms of the Apache License, Version
  # 2.0, and the BSD License. See the LICENSE file in the root of this repository
  # for complete details.
  
  from __future__ import absolute_import, division, print_function
  
  import hmac
  import warnings
  
  from cryptography import utils
  from cryptography.hazmat.bindings._constant_time import lib
  
  
  if hasattr(hmac, "compare_digest"):
      def bytes_eq(a, b):
          if not isinstance(a, bytes) or not isinstance(b, bytes):
              raise TypeError("a and b must be bytes.")
  
          return hmac.compare_digest(a, b)
  
  else:
      warnings.warn(
          "Support for your Python version is deprecated. The next version of "
          "cryptography will remove support. Please upgrade to a 2.7.x "
          "release that supports hmac.compare_digest as soon as possible.",
          utils.PersistentlyDeprecated2018,
      )
  
      def bytes_eq(a, b):
          if not isinstance(a, bytes) or not isinstance(b, bytes):
              raise TypeError("a and b must be bytes.")
  
          return lib.Cryptography_constant_time_bytes_eq(
              a, len(a), b, len(b)
          ) == 1
  