commit 483e985e487aadc20818085fc196f1819800ebc6
Author: Robert Collins <rbtcollins@hp.com>
Date:   Mon Jan 19 14:57:35 2015 +1300

    Issue #17911: Avoid spurious linecache checks.
    
    The traceback module was statting every file once per frame, not once per
    traceback.

diff --git a/Lib/traceback.py b/Lib/traceback.py
index 686bd80..321155e 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -54,6 +54,8 @@ def _extract_tb_or_stack_iter(curr, limit, extractor):
     if limit is None:
         limit = getattr(sys, 'tracebacklimit', None)
 
+    result = []
+    fnames = set()
     n = 0
     while curr is not None and (limit is None or n < limit):
         f, lineno, next_item = extractor(curr)
@@ -61,12 +63,15 @@ def _extract_tb_or_stack_iter(curr, limit, extractor):
         filename = co.co_filename
         name = co.co_name
 
-        linecache.checkcache(filename)
+        fnames.add(filename)
         line = linecache.deferredcache(filename, f.f_globals)
 
-        yield Frame(filename, lineno, name)
+        result.append(Frame(filename, lineno, name))
         curr = next_item
         n += 1
+    for filename in fnames:
+        linecache.checkcache(filename)
+    return result
 
 def _extract_tb_iter(tb, limit):
     return _extract_tb_or_stack_iter(