Recipe package system.

recipe_engine/types.py

+# Copyright 2015 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.
+
+import collections
+import operator
+
+
+def freeze(obj):
+  """Takes a generic object ``obj``, and returns an immutable version of it.
+
+  Supported types:
+    * dict / OrderedDict -> FrozenDict
+    * list -> tuple
+    * set -> frozenset
+    * any object with a working __hash__ implementation (assumes that hashable
+      means immutable)
+
+  Will raise TypeError if you pass an object which is not hashable.
+  """
+  if isinstance(obj, dict):
+    return FrozenDict((freeze(k), freeze(v)) for k, v in obj.iteritems())
+  elif isinstance(obj, (list, tuple)):
+    return tuple(freeze(i) for i in obj)
+  elif isinstance(obj, set):
+    return frozenset(freeze(i) for i in obj)
+  else:
+    hash(obj)
+    return obj
+
+
+class FrozenDict(collections.Mapping):
+  """An immutable OrderedDict.
+
+  Modified From: http://stackoverflow.com/a/2704866
+  """
+  def __init__(self, *args, **kwargs):
+    self._d = collections.OrderedDict(*args, **kwargs)
+
+    # Calculate the hash immediately so that we know all the items are
+    # hashable too.
+    self._hash = reduce(operator.xor,
+                        (hash(i) for i in enumerate(self._d.iteritems())), 0)
+
+  def __eq__(self, other):
+    if not isinstance(other, collections.Mapping):
+      return NotImplemented
+    if self is other:
+      return True
+    if len(self) != len(other):
+      return False
+    for k, v in self.iteritems():
+      if k not in other or other[k] != v:
+        return False
+    return True
+
+  def __iter__(self):
+    return iter(self._d)
+
+  def __len__(self):
+    return len(self._d)
+
+  def __getitem__(self, key):
+    return self._d[key]
+
+  def __hash__(self):
+    return self._hash
+
+  def __repr__(self):
+    return 'FrozenDict(%r)' % (self._d.items(),)