Extensions Docs Server: Internal file system

chrome/common/extensions/docs/server2/future.py

+# Copyright (c) 2012 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+_no_value = object()
+
+class Future(object):
+  """Stores a value, error, or delegate to be used later.
+  """
+  def __init__(self, value=_no_value, error=None, delegate=None):
+    self._value = value
+    self._error = error
+    self._delegate = delegate
+    if (self._value is _no_value and
+        self._error is None and
+        self._delegate is None):
+      raise ValueError('Must have either a value, error, or delegate.')
+
+  def Get(self):
+    """Gets the stored value, error, or delegate contents.
+    """
+    if self._value is not _no_value:
+      return self._value
+    if self._error is not None:
+      raise self._error
+    try:
+      self._value = self._delegate.Get()
+    except Exception as self._error:
+      raise
+    return self._value