Refactor infra git libs and testing.

infra/libs/data_structures/data_structures.py

+# Copyright 2014 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

[Vadim Sh., 2014/06/27 18:26:22]

nit: \n

[iannucci, 2014/06/28 08:33:35]

Done.

+import operator
+
+
+def freeze(obj):

[Vadim Sh., 2014/06/27 18:26:22]

if |obj| is already frozen, it makes a copy. In theory it's not necessary.

[iannucci, 2014/06/28 08:33:35]

Don't think this is the case

+  """Takes a jsonish object |obj|, and returns an immutable version of it."""

[Vadim Sh., 2014/06/27 18:26:22]

There's no asserts anywhere that verify it's 'jsonish' object. I can pass object
of some user defined classes here as long as they define __hash__. 

[iannucci, 2014/06/28 08:33:35]

Clarified in the comment

+  if isinstance(obj, dict):
+    return FrozenDict((freeze(k), freeze(v)) for k, v in obj.iteritems())
+  elif isinstance(obj, list):

[Vadim Sh., 2014/06/27 18:26:22]

tuples with non-frozen items will not be frozen.

elif isinstance(obj, (list, tuple))?

[iannucci, 2014/06/28 08:33:35]

Done.

+    return tuple(freeze(i) for i in obj)
+  elif isinstance(obj, set):
+    return frozenset(freeze(i) for i in obj)
+  else:
+    hash(obj)

[Vadim Sh., 2014/06/27 18:26:21]

assert getattr(obj, '__hash__' , None), 'Can\'t freeze unhashable type'

no need to actually calculate the hash, right?

[iannucci, 2014/06/28 08:33:35]

it recurses, so 'guarantees' that all objects inside are also hashable.

+    return obj
+
+
+def thaw(obj):
+  """Takes an object from freeze() and returns a mutable copy of it."""
+  if isinstance(obj, FrozenDict):
+    return collections.OrderedDict(
+        (thaw(k), thaw(v)) for k, v in obj.iteritems())
+  elif isinstance(obj, tuple):
+    return list(thaw(i) for i in obj)

[Vadim Sh., 2014/06/27 18:26:22]

distinction between tuples and lists will be lost after freeze\thaw :(

[iannucci, 2014/06/28 08:33:35]

disinclined to care... that seems like a much harder problem and these are
supposed to just be light helper methods. :)

+  elif isinstance(obj, frozenset):
+    return set(thaw(i) for i in obj)
+  else:
+    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)
+    self._hash = reduce(operator.xor,

[Vadim Sh., 2014/06/27 18:26:22]

Why not make it lazy?

[iannucci, 2014/06/28 08:33:35]

Added comment

+                        (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(),)