取得環境配置變數，環境變數設定提示問題獲得環境變數值，只能為True或False
def get_var(environ_cp,
            var_name,
            query_item,
            enabled_by_default,
            question=None,
            yes_reply=None,
            no_reply=None):
  """Get boolean input from user.

  If var_name is not set in env, ask user to enable query_item or not. If the
  response is empty, use the default.

  Args:
    environ_cp: copy of the os.environ.
    var_name: string for name of environment variable, e.g. "TF_NEED_HDFS".
    query_item: string for feature related to the variable, e.g. "Hadoop File
      System".
    enabled_by_default: boolean for default behavior.
    question: optional string for how to ask for user input.
    yes_reply: optional string for reply when feature is enabled.
    no_reply: optional string for reply when feature is disabled.

  Returns:
    boolean value of the variable.

  Raises:
    UserInputError: if an environment variable is set, but it cannot be
      interpreted as a boolean indicator, assume that the user has made a
      scripting error, and will continue to provide invalid input.
      Raise the error to avoid infinitely looping.
  """
  if not question:
    question = 'Do you wish to build TensorFlow with %s support?' % query_item
  if not yes_reply:
    yes_reply = '%s support will be enabled for TensorFlow.' % query_item
  if not no_reply:
    no_reply = 'No %s' % yes_reply

  yes_reply += '\n'
  no_reply += '\n'

  if enabled_by_default:
    question += ' [Y/n]: '
  else:
    question += ' [y/N]: '

  var = environ_cp.get(var_name)
  if var is not None:
    var_content = var.strip().lower()
    true_strings = ('1', 't', 'true', 'y', 'yes')
    false_strings = ('0', 'f', 'false', 'n', 'no')
    if var_content in true_strings:
      var = True
    elif var_content in false_strings:
      var = False
    else:
      raise UserInputError(
          'Environment variable %s must be set as a boolean indicator.\n'
          'The following are accepted as TRUE : %s.\n'
          'The following are accepted as FALSE: %s.\n'
          'Current value is %s.' % (
              var_name, ', '.join(true_strings), ', '.join(false_strings),
              var))

  while var is None:
    user_input_origin = get_input(question)
    user_input = user_input_origin.strip().lower()
    if user_input == 'y':
      print(yes_reply)
      var = True
    elif user_input == 'n':
      print(no_reply)
      var = False
    elif not user_input:
      if enabled_by_default:
        print(yes_reply)
        var = True
      else:
        print(no_reply)
        var = False
    else:
      print('Invalid selection: %s' % user_input_origin)
  return var

設定編譯變數
def set_build_var(environ_cp, var_name, query_item, option_name,
                  enabled_by_default, bazel_config_name=None):
  """Set if query_item will be enabled for the build.

  Ask user if query_item will be enabled. Default is used if no input is given.
  Set subprocess environment variable and write to .bazelrc if enabled.

  Args:
    environ_cp: copy of the os.environ.
    var_name: string for name of environment variable, e.g. "TF_NEED_HDFS".
    query_item: string for feature related to the variable, e.g. "Hadoop File
      System".
    option_name: string for option to define in .bazelrc.
    enabled_by_default: boolean for default behavior.
    bazel_config_name: Name for Bazel --config argument to enable build feature.
  """

  var = str(int(get_var(environ_cp, var_name, query_item, enabled_by_default)))
  environ_cp[var_name] = var
  if var == '1':
    write_to_bazelrc('build --define %s=true' % option_name)
  elif bazel_config_name is not None:
    # TODO(mikecase): Migrate all users of configure.py to use --config Bazel
    # options and not to set build configs through environment variables.
    write_to_bazelrc('build:%s --define %s=true'
                     % (bazel_config_name, option_name))

設定動作變數，通過get_var獲取環境配置變數值，寫入bazelrc
def set_action_env_var(environ_cp,
                       var_name,
                       query_item,
                       enabled_by_default,
                       question=None,
                       yes_reply=None,
                       no_reply=None):
  """Set boolean action_env variable.

  Ask user if query_item will be enabled. Default is used if no input is given.
  Set environment variable and write to .bazelrc.

  Args:
    environ_cp: copy of the os.environ.
    var_name: string for name of environment variable, e.g. "TF_NEED_HDFS".
    query_item: string for feature related to the variable, e.g. "Hadoop File
      System".
    enabled_by_default: boolean for default behavior.
    question: optional string for how to ask for user input.
    yes_reply: optional string for reply when feature is enabled.
    no_reply: optional string for reply when feature is disabled.
  """
  var = int(
      get_var(environ_cp, var_name, query_item, enabled_by_default, question,
              yes_reply, no_reply))

  write_action_env_to_bazelrc(var_name, var)
  environ_cp[var_name] = str(var)

轉換版本號為int型
def convert_version_to_int(version):
  """Convert a version number to a integer that can be used to compare.

  Version strings of the form X.YZ and X.Y.Z-xxxxx are supported. The
  'xxxxx' part, for instance 'homebrew' on OS/X, is ignored.

  Args:
    version: a version to be converted

  Returns:
    An integer if converted successfully, otherwise return None.
  """
  version = version.split('-')[0]
  version_segments = version.split('.')
  for seg in version_segments:
    if not seg.isdigit():
      return None

  version_str = ''.join(['%03d' % int(seg) for seg in version_segments])
  return int(version_str)

#檢查編譯工作版本號
def check_bazel_version(min_version):
  """Check installed bazel version is at least min_version.

  Args:
    min_version: string for minimum bazel version.

  Returns:
    The bazel version detected.
  """
  if which('bazel') is None:
    print('Cannot find bazel. Please install bazel.')
    sys.exit(0)
  curr_version = run_shell(['bazel', '--batch', '--bazelrc=/dev/null', 'version'])

  for line in curr_version.split('\n'):
    if 'Build label: ' in line:
      curr_version = line.split('Build label: ')[1]
      break

  min_version_int = convert_version_to_int(min_version)
  curr_version_int = convert_version_to_int(curr_version)

  # Check if current bazel version can be detected properly.
  if not curr_version_int:
    print('WARNING: current bazel installation is not a release version.')
    print('Make sure you are running at least bazel %s' % min_version)
    return curr_version

  print('You have bazel %s installed.' % curr_version)

  if curr_version_int < min_version_int:
    print('Please upgrade your bazel installation to version %s or higher to '
          'build TensorFlow!' % min_version)
    sys.exit(0)
  return curr_version