--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/piecrust/templating/jinja/loader.py	Sat Apr 29 21:42:22 2017 -0700
@@ -0,0 +1,24 @@
+import os.path
+from jinja2 import FileSystemLoader
+
+
+class PieCrustLoader(FileSystemLoader):
+    def __init__(self, searchpath, encoding='utf-8'):
+        super(PieCrustLoader, self).__init__(searchpath, encoding)
+        self.segment_parts_cache = {}
+
+    def get_source(self, environment, template):
+        if template.startswith('$part='):
+            filename, seg_part = self.segment_parts_cache[template]
+
+            mtime = os.path.getmtime(filename)
+
+            def uptodate():
+                try:
+                    return os.path.getmtime(filename) == mtime
+                except OSError:
+                    return False
+
+            return seg_part, filename, uptodate
+
+        return super(PieCrustLoader, self).get_source(environment, template)