diff -r aeb3faaf4754 Lib/tempfile.py
--- a/Lib/tempfile.py	Mon Sep 02 17:01:10 2013 -0700
+++ b/Lib/tempfile.py	Thu Sep 05 09:36:05 2013 +0100
@@ -27,6 +27,7 @@
 
 # Imports.
 
+import functools as _functools
 import warnings as _warnings
 import sys as _sys
 import io as _io
@@ -344,7 +345,16 @@
         a = getattr(file, name)
         if not isinstance(a, int):
             setattr(self, name, a)
-        return a
+
+        if hasattr(a, '__call__'):
+            @_functools.wraps(a)
+            def func_wrapper(*args, **kwargs):
+                # This is to prevent self getting out of scope too early, see bug 18879
+                local_self_copy = self
+                return a(*args, **kwargs)
+
+            return func_wrapper
+        else:
+            return a
 
     # The underlying __enter__ method returns the wrong object
     # (self.file) so override it to return the wrapper
diff -r aeb3faaf4754 Lib/test/test_tempfile.py
--- a/Lib/test/test_tempfile.py	Mon Sep 02 17:01:10 2013 -0700
+++ b/Lib/test/test_tempfile.py	Thu Sep 05 09:36:05 2013 +0100
@@ -610,6 +610,9 @@
         self.do_create(pre="a", suf="b")
         self.do_create(pre="aa", suf=".txt")
 
+    def test_regression_18879(self):
+        self.do_create().write(b"xxx")
+
     def test_creates_named(self):
         # NamedTemporaryFile creates files with names
         f = tempfile.NamedTemporaryFile()