gistfile1.py

diff --git a/scrapy/selector/unified.py b/scrapy/selector/unified.py
index b8a3678..6ce1de1 100644
--- a/scrapy/selector/unified.py
+++ b/scrapy/selector/unified.py
@@ -46,10 +46,40 @@ def _response_from_text(text, st):
               body=unicode_to_str(text, 'utf-8'))
 
 
+import threading
+data = threading.local()
+data.selector = None
+class SelectorContext(object):
+
+    def __init__(self, selector):
+        self._selector = selector
+        self._last = None
+
+    def __enter__(self):
+        self._last = data.selector
+        data.selector = self._selector
+
+    def __exit__(self, type, value, traceback):
+        data.selector = self._last
+
+from functools import wraps
+
+
+def selectorcontext(func):
+    @wraps(func)
+    def wrapper(**kwargs):
+        if 'selector' not in kwargs:
+            selector = data.selector
+            if selector is not None:
+                kwargs['selector'] = selector
+        return func(**kwargs)
+    return wrapper
+
+
 class Selector(object_ref):
 
     __slots__ = ['response', 'text', 'namespaces', 'type', '_expr', '_root',
-                 '__weakref__', '_parser', '_csstranslator', '_tostring_method']
+                 '__weakref__', '_parser', '_csstranslator', '_tostring_method', '_contextmanager']
 
     _default_type = None
     _default_namespaces = {
@@ -84,6 +114,15 @@ class Selector(object_ref):
             self.namespaces.update(namespaces)
         self._root = _root
         self._expr = _expr
+        self._contextmanager = None
+
+    def __enter__(self):
+        self._contextmanager = SelectorContext(self)
+        self._contextmanager.__enter__()
+        return self
+
+    def __exit__(self, type, value, traceback):
+        self._contextmanager.__exit__(type, value, traceback)
 
     def xpath(self, query):
         try:
@@ -163,10 +202,24 @@ class Selector(object_ref):
 
 class SelectorList(list):
 
+    def __init__(self, *args, **kwargs):
+        super(SelectorList, self).__init__(*args, **kwargs)
+        self._contextmanager = None
+
     def __getslice__(self, i, j):
         return self.__class__(list.__getslice__(self, i, j))
 
+    def __enter__(self):
+        self._contextmanager = SelectorContext(self)
+        self._contextmanager.__enter__()
+        return self
+
+    def __exit__(self, type, value, traceback):
+        self._contextmanager.__exit__(type, value, traceback)
+
     def xpath(self, xpath):
+        if self._contextmanager is not None:
+            return self._contextmanager._selector.xpath(xpath)
         return self.__class__(flatten([x.xpath(xpath) for x in self]))
 
     def css(self, xpath):