Make variable ordering deterministic

3 files changed, 90 insertions, 3 deletions

diff --git a/uritemplate/api.py b/uritemplate/api.py
index 37c7c45..5ad2815 100644
--- a/uritemplate/api.py
+++ b/uritemplate/api.py
@@ -6,6 +6,8 @@ uritemplate.api
 This module contains the very simple API provided by uritemplate.
 
 """
+
+from uritemplate.orderedset import OrderedSet
 from uritemplate.template import URITemplate
 
 
@@ -68,4 +70,4 @@ def variables(uri):
         # => {'username', 'repository'}
 
     """
-    return set(URITemplate(uri).variable_names)
+    return OrderedSet(URITemplate(uri).variable_names)
diff --git a/uritemplate/orderedset.py b/uritemplate/orderedset.py
new file mode 100644
index 0000000..94f4733
--- /dev/null
+++ b/uritemplate/orderedset.py
@@ -0,0 +1,83 @@
+# From: https://github.com/ActiveState/code/blob/master/recipes/Python/576696_OrderedSet_with_Weakrefs/
+
+import collections
+from weakref import proxy
+
+class Link(object):
+    __slots__ = 'prev', 'next', 'key', '__weakref__'
+
+class OrderedSet(collections.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)
diff --git a/uritemplate/template.py b/uritemplate/template.py
index ceca8eb..0df0da6 100644
--- a/uritemplate/template.py
+++ b/uritemplate/template.py
@@ -16,6 +16,7 @@ What do you do?
 """
 
 import re
+from uritemplate.orderedset import OrderedSet
 from uritemplate.variable import URIVariable
 
 template_re = re.compile('{([^}]+)}')
@@ -71,9 +72,10 @@ class URITemplate(object):
             URIVariable(m.groups()[0]) for m in template_re.finditer(self.uri)
         ]
         #: A set of variable names in the URI.
-        self.variable_names = set()
+        self.variable_names = OrderedSet()
         for variable in self.variables:
-            self.variable_names.update(variable.variable_names)
+            for name in variable.variable_names:
+                self.variable_names.add(name)
 
     def __repr__(self):
         return 'URITemplate("%s")' % self