From 49d68cefa5aa1ea617a2d6be5ee1444b4efb20cb Mon Sep 17 00:00:00 2001
From: foefl <f.foerster@d-opt.com>
Date: Mon, 23 Mar 2026 11:21:53 +0100
Subject: [PATCH] add symmetric iteration routine, related to #5

---
 src/dopt_basics/iteration.py | 19 +++++++++++++++++++
 tests/test_iteration.py      | 25 +++++++++++++++++++++++++
 2 files changed, 44 insertions(+)
 create mode 100644 src/dopt_basics/iteration.py
 create mode 100644 tests/test_iteration.py

diff --git a/src/dopt_basics/iteration.py b/src/dopt_basics/iteration.py
new file mode 100644
index 0000000..185c4d3
--- /dev/null
+++ b/src/dopt_basics/iteration.py
@@ -0,0 +1,19 @@
+from __future__ import annotations
+
+from collections import deque
+from collections.abc import Iterator, Sequence
+from typing import TypeVar
+
+T = TypeVar("T")
+
+
+def symmetric_iter(
+    x: Sequence[T],
+) -> Iterator[T]:
+    d = deque(x)
+
+    for idx in range(len(d)):
+        if idx % 2 == 0:
+            yield d.popleft()
+        else:
+            yield d.pop()
diff --git a/tests/test_iteration.py b/tests/test_iteration.py
new file mode 100644
index 0000000..7ace088
--- /dev/null
+++ b/tests/test_iteration.py
@@ -0,0 +1,25 @@
+from dopt_basics import iteration
+
+
+def test_symmetric_iter_1():
+    l1_in = [1, 2, 3, 4, 5, 6]
+    l1_out = [1, 6, 2, 5, 3, 4]
+
+    l1_calc = list(iteration.symmetric_iter(l1_in))
+    assert len(l1_in) == len(l1_calc)
+    assert len(l1_out) == len(l1_calc)
+
+    for truth, calc in zip(l1_out, l1_calc):
+        assert truth == calc
+
+
+def test_symmetric_iter_2():
+    l1_in = [1, 2, 3, 4, 5]
+    l1_out = [1, 5, 2, 4, 3]
+
+    l1_calc = list(iteration.symmetric_iter(l1_in))
+    assert len(l1_in) == len(l1_calc)
+    assert len(l1_out) == len(l1_calc)
+
+    for truth, calc in zip(l1_out, l1_calc):
+        assert truth == calc