Allow for circular nth

4 files changed, 25 insertions, 6 deletions

diff --git a/scss/functions/core.py b/scss/functions/core.py
index b1fb6a0..e916aca 100644
--- a/scss/functions/core.py
+++ b/scss/functions/core.py
@@ -593,7 +593,8 @@ def nth(lst, n):
         else:
             raise ValueError("Invalid index %r" % (n,))
     else:
-        i = n.to_python_index(len(lst))
+        # DEVIATION: nth treats lists as circular lists
+        i = n.to_python_index(len(lst), circular=True)
 
     return lst[i]
 
diff --git a/scss/tests/files/kronuz/lists-circular-nth.css b/scss/tests/files/kronuz/lists-circular-nth.css
new file mode 100644
index 0000000..9cefdef
--- /dev/null
+++ b/scss/tests/files/kronuz/lists-circular-nth.css
@@ -0,0 +1,6 @@
+div {
+  margin-top: 4px;
+  margin-right: 2px;
+  margin-bottom: 4px;
+  margin-left: 2px;
+}
diff --git a/scss/tests/files/kronuz/lists-circular-nth.scss b/scss/tests/files/kronuz/lists-circular-nth.scss
new file mode 100644
index 0000000..851a305
--- /dev/null
+++ b/scss/tests/files/kronuz/lists-circular-nth.scss
@@ -0,0 +1,9 @@
+@option style:legacy;
+
+div {
+	$list: 4px 2px;
+	margin-top: nth($list, 1);
+	margin-right: nth($list, 2);
+	margin-bottom: nth($list, 3);
+	margin-left: nth($list, 4);
+}
diff --git a/scss/types.py b/scss/types.py
index 3351f7f..d0079d3 100644
--- a/scss/types.py
+++ b/scss/types.py
@@ -462,7 +462,7 @@ class Number(Value):
 
         return wrapped
 
-    def to_python_index(self, length, check_bounds=True):
+    def to_python_index(self, length, check_bounds=True, circular=False):
         """Return a plain Python integer appropriate for indexing a sequence of
         the given length.  Raise if this is impossible for any reason
         whatsoever.
@@ -477,13 +477,16 @@ class Number(Value):
         if ret == 0:
             raise ValueError("Index cannot be zero")
 
-        if check_bounds and abs(ret) > length:
+        if check_bounds and not circular and abs(ret) > length:
             raise ValueError("Index {0!r} out of bounds for length {1}".format(ret, length))
 
         if ret > 0:
-            return ret - 1
-        else:
-            return ret
+            ret -= 1
+
+        if circular:
+            ret = ret % length
+
+        return ret
 
     @property
     def has_simple_unit(self):