# HG changeset patch

diff --git a/Lib/traceback.py b/Lib/traceback.py
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -3,6 +3,8 @@
 import linecache
 import sys
 import operator
+import types
+import collections
 
 __all__ = ['extract_stack', 'extract_tb', 'format_exception',
            'format_exception_only', 'format_list', 'format_stack',
@@ -51,7 +53,14 @@
 # - Next item (same type as curr)
 # In practice, curr is either a traceback or a frame.
 def _extract_tb_or_stack_iter(curr, limit, extractor):
-    if limit is None:
+    # Check if limit is negative and curr is a traceback
+    condition = limit is not None and limit < 0 \
+                and isinstance(curr, types.TracebackType)
+    # Collect last abs(limit) traceback entries. O(1) for pop operations
+    if condition:
+        seq = collections.deque(maxlen=abs(limit))
+
+    if limit is None or condition:
         limit = getattr(sys, 'tracebacklimit', None)
 
     n = 0
@@ -61,18 +70,25 @@
         filename = co.co_filename
         name = co.co_name
 
-        linecache.checkcache(filename)
-        line = linecache.getline(filename, lineno, f.f_globals)
+        if not condition:
+            # Positive limit; load source immediately
+            linecache.checkcache(filename)
+            line = linecache.getline(filename, lineno, f.f_globals)
+            yield (filename, lineno, name, line.strip() if line else None)
+        else:
+            # Negative limit; load source after the loop. The last tuple 
+            # element is a frame globals
+            seq.append((filename, lineno, name, f.f_globals))
 
-        if line:
-            line = line.strip()
-        else:
-            line = None
-
-        yield (filename, lineno, name, line)
         curr = next_item
         n += 1
 
+    if condition:
+        for filename, lineno, name, f_globals in seq:
+            linecache.checkcache(filename)
+            line = linecache.getline(filename, lineno, f_globals)
+            yield (filename, lineno, name, line.strip() if line else None)
+
 def _extract_tb_iter(tb, limit):
     return _extract_tb_or_stack_iter(
                 tb, limit,