1 files changed, 90 insertions, 0 deletions
diff --git a/uritemplate/orderedset.py b/uritemplate/orderedset.py
new file mode 100644
index 0000000..f21c9cb
--- /dev/null
+++ b/uritemplate/orderedset.py
@@ -0,0 +1,90 @@
+# From: https://github.com/ActiveState/code/blob/master/recipes/Python/576696_OrderedSet_with_Weakrefs/  # noqa
+
+from weakref import proxy
+
+try:
+    import collections.abc as collections_abc
+except ImportError:
+    import collections as collections_abc
+
+
+class Link(object):
+    __slots__ = 'prev', 'next', 'key', '__weakref__'
+
+
+class OrderedSet(collections_abc.MutableSet):
+    'Set the remembers the order elements were added'
+    # Big-O running times for all methods are the same as for regular sets.
+    # The internal self.__map dictionary maps keys to links in a doubly linked
+    # list. The circular doubly linked list starts and ends with a sentinel
+    # element. The sentinel element never gets deleted (this simplifies the
+    # algorithm). The prev/next links are weakref proxies (to prevent circular
+    # references). Individual links are kept alive by the hard reference in
+    # self.__map. Those hard references disappear when a key is deleted from
+    # an OrderedSet.
+
+    def __init__(self, iterable=None):
+        self.__root = root = Link()  # sentinel node for doubly linked list
+        root.prev = root.next = root
+        self.__map = {}  # key --> link
+        if iterable is not None:
+            self |= iterable
+
+    def __len__(self):
+        return len(self.__map)
+
+    def __contains__(self, key):
+        return key in self.__map
+
+    def add(self, key):
+        # Store new key in a new link at the end of the linked list
+        if key not in self.__map:
+            self.__map[key] = link = Link()
+            root = self.__root
+            last = root.prev
+            link.prev, link.next, link.key = last, root, key
+            last.next = root.prev = proxy(link)
+
+    def discard(self, key):
+        # Remove an existing item using self.__map to find the link which is
+        # then removed by updating the links in the predecessor and successors.
+        if key in self.__map:
+            link = self.__map.pop(key)
+            link.prev.next = link.next
+            link.next.prev = link.prev
+
+    def __iter__(self):
+        # Traverse the linked list in order.
+        root = self.__root
+        curr = root.next
+        while curr is not root:
+            yield curr.key
+            curr = curr.next
+
+    def __reversed__(self):
+        # Traverse the linked list in reverse order.
+        root = self.__root
+        curr = root.prev
+        while curr is not root:
+            yield curr.key
+            curr = curr.prev
+
+    def pop(self, last=True):
+        if not self:
+            raise KeyError('set is empty')
+        key = next(reversed(self)) if last else next(iter(self))
+        self.discard(key)
+        return key
+
+    def __repr__(self):
+        if not self:
+            return '%s()' % (self.__class__.__name__,)
+        return '%s(%r)' % (self.__class__.__name__, list(self))
+
+    def __str__(self):
+        return self.__repr__()
+
+    def __eq__(self, other):
+        if isinstance(other, OrderedSet):
+            return len(self) == len(other) and list(self) == list(other)
+        return not self.isdisjoint(other)