1 files changed, 56 insertions, 0 deletions
diff --git a/setuptools/_distutils/_collections.py b/setuptools/_distutils/_collections.py
new file mode 100644
index 0000000..98fce80
--- /dev/null
+++ b/setuptools/_distutils/_collections.py
@@ -0,0 +1,56 @@
+import collections
+import itertools
+
+
+# from jaraco.collections 3.5.1
+class DictStack(list, collections.abc.Mapping):
+    """
+    A stack of dictionaries that behaves as a view on those dictionaries,
+    giving preference to the last.
+
+    >>> stack = DictStack([dict(a=1, c=2), dict(b=2, a=2)])
+    >>> stack['a']
+    2
+    >>> stack['b']
+    2
+    >>> stack['c']
+    2
+    >>> len(stack)
+    3
+    >>> stack.push(dict(a=3))
+    >>> stack['a']
+    3
+    >>> set(stack.keys()) == set(['a', 'b', 'c'])
+    True
+    >>> set(stack.items()) == set([('a', 3), ('b', 2), ('c', 2)])
+    True
+    >>> dict(**stack) == dict(stack) == dict(a=3, c=2, b=2)
+    True
+    >>> d = stack.pop()
+    >>> stack['a']
+    2
+    >>> d = stack.pop()
+    >>> stack['a']
+    1
+    >>> stack.get('b', None)
+    >>> 'c' in stack
+    True
+    """
+
+    def __iter__(self):
+        dicts = list.__iter__(self)
+        return iter(set(itertools.chain.from_iterable(c.keys() for c in dicts)))
+
+    def __getitem__(self, key):
+        for scope in reversed(tuple(list.__iter__(self))):
+            if key in scope:
+                return scope[key]
+        raise KeyError(key)
+
+    push = list.append
+
+    def __contains__(self, other):
+        return collections.abc.Mapping.__contains__(self, other)
+
+    def __len__(self):
+        return len(list(iter(self)))