--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/CodonSwitchTool/cachingseq.py	Tue May 21 05:24:56 2019 -0400
@@ -0,0 +1,55 @@
+#!/usr/bin/env python2
+#
+# Copyright 2011-2016 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# vim: sw=2 sts=2 et
+
+class CachingFuncSequence(object):
+    def __init__(self, func, length, inc_func=None):
+        """
+        length: Length of this sequence.
+        func: function(index)
+        inc_func: function(index, value_of_previous)
+        """
+
+        self.func = func
+        self.inc_func = inc_func
+        self.length = length
+        self._cache = {}
+
+    def __getitem__(self, i):
+        if i < 0:
+            i += self.length
+        if i < 0 or i >= self.length:
+            raise IndexError()
+
+        v = self._cache.get(i)
+        if v is not None:
+            return v
+
+        if self.inc_func and i-1 in self._cache:
+            v = self.inc_func(i, self._cache[i-1])
+        else:
+            v = self.func(i)
+
+        self._cache[i] = v
+        return v
+
+    def __len__(self):
+        return self.length
+
+    def __iter__(self):
+        for i in range(self.length):
+            yield self[i]