Patch #1550800: make exec a function.
diff --git a/Doc/lib/libtraceback.tex b/Doc/lib/libtraceback.tex
index 80dc423..a87b1ef 100644
--- a/Doc/lib/libtraceback.tex
+++ b/Doc/lib/libtraceback.tex
@@ -139,7 +139,7 @@
 def run_user_code(envdir):
     source = raw_input(">>> ")
     try:
-        exec source in envdir
+        exec(source, envdir)
     except:
         print "Exception in user code:"
         print '-'*60