[Cuprit-finder] Add MetaDict class.

appengine/findit/libs/meta_object.py

+# Copyright 2017 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.
+
+
+class MetaObject(object):
+  """Class that can be either one element or a collection of elements."""
+
+  def IsElement(self):  # pragma: no cover
+    return NotImplementedError()
+
+
+class Element(MetaObject):
+  """Element class that cannot be divided anymore."""
+
+  @property
+  def is_element(self):
+    return True
+
+
+class MetaDict(MetaObject):
+  """Dict-like object containing a collection of ``MetaObject``s."""
+
+  def __init__(self, value):
+    """Construct a meta dict from a dict of meta objects.
+
+    Args:
+      value (dict): Dict of meta objects.
+    """
+    self._value = value

[chanli, 2017/01/22 00:07:20]

So what I meant in meta_object_test.py is that I don't know if you should use
deepcopy here? Otherwise will the operation on a MetaDict object affect the
value dict as well? Or is it expected?

[Sharu Jiang, 2017/01/23 20:45:40]

Good point, it is safer to make deepcopy here.

+
+  @property
+  def is_element(self):
+    return False
+
+  def __getitem__(self, key):
+    return self._value[key]
+
+  def __setitem__(self, key, val):
+    self._value[key] = val
+
+  def get(self, key, default=None):
+    return self._value.get(key, default)
+
+  def __iter__(self):
+    return iter(self._value)
+
+  def __eq__(self, other):
+    return self._value == other._value
+
+  def iteritems(self):
+    return self._value.iteritems()
+
+  def itervalues(self):
+    return self._value.itervalues()
+
+  def keys(self):
+    return self._value.keys()
+
+  def values(self):
+    return self._value.values()