Issue 2021: Allow NamedTemporaryFile and SpooledTemporaryFile to be used as context managers. (The NamedTemporaryFile fix should be considered for backporting to 2.5)

Doc/library/tempfile.rst

@@ -51,7 +51,8 @@ The module defines the following user-callable functions:
 
    The returned object is a true file object on POSIX platforms.  On other
    platforms, it is a file-like object whose :attr:`file` attribute is the
-   underlying true file object.
+   underlying true file object. This file-like object can be used in a :keyword:`with`
+   statement, just like a normal file.
 
 
 .. function:: NamedTemporaryFile([mode='w+b'[, bufsize=-1[, suffix[, prefix[, dir[, delete]]]]]])
@@ -65,7 +66,8 @@ The module defines the following user-callable functions:
    If *delete* is true (the default), the file is deleted as soon as it is closed.
 
    The returned object is always a file-like object whose :attr:`file` attribute
-   is the underlying true file object.
+   is the underlying true file object. This file-like object can be used in a :keyword:`with`
+   statement, just like a normal file.
 
    .. versionadded:: 2.3
 
@@ -85,7 +87,8 @@ The module defines the following user-callable functions:
 
    The returned object is a file-like object whose :attr:`_file` attribute
    is either a :class:`StringIO` object or a true file object, depending on
-   whether :func:`rollover` has been called.
+   whether :func:`rollover` has been called. This file-like object can be used in a
+   :keyword:`with` statement, just like a normal file.
 
    .. versionadded:: 2.6
 

Lib/tempfile.py

@@ -370,6 +370,7 @@ def mktemp(suffix="", prefix=template, dir=None):
 
     raise IOError, (_errno.EEXIST, "No usable temporary filename found")
 
+
 class _TemporaryFileWrapper:
     """Temporary file wrapper
 
@@ -385,17 +386,25 @@ class _TemporaryFileWrapper:
         self.delete = delete
 
     def __getattr__(self, name):
+        # Attribute lookups are delegated to the underlying file
+        # and cached for non-numeric results
+        # (i.e. methods are cached, closed and friends are not)
         file = self.__dict__['file']
         a = getattr(file, name)
-        if type(a) != type(0):
+        if not issubclass(type(a), type(0)):
             setattr(self, name, a)
         return a
 
+    # The underlying __enter__ method returns the wrong object
+    # (self.file) so override it to return the wrapper
+    def __enter__(self):
+        self.file.__enter__()
+        return self
+
     # NT provides delete-on-close as a primitive, so we don't need
     # the wrapper to do anything special.  We still use it so that
     # file.name is useful (i.e. not "(fdopen)") with NamedTemporaryFile.
     if _os.name != 'nt':
-
         # Cache the unlinker so we don't get spurious errors at
         # shutdown when the module-level "os" is None'd out.  Note
         # that this must be referenced as self.unlink, because the
@@ -413,6 +422,14 @@ class _TemporaryFileWrapper:
         def __del__(self):
             self.close()
 
+        # Need to trap __exit__ as well to ensure the file gets
+        # deleted when used in a with statement
+        def __exit__(self, exc, value, tb):
+            result = self.file.__exit__(exc, value, tb)
+            self.close()
+            return result
+
+
 def NamedTemporaryFile(mode='w+b', bufsize=-1, suffix="",
                        prefix=template, dir=None, delete=True):
     """Create and return a temporary file.
@@ -511,6 +528,20 @@ class SpooledTemporaryFile:
 
         self._rolled = True
 
+    # The method caching trick from NamedTemporaryFile
+    # won't work here, because _file may change from a
+    # _StringIO instance to a real file. So we list
+    # all the methods directly.
+
+    # Context management protocol
+    def __enter__(self):
+        if self._file.closed:
+            raise ValueError("Cannot enter context with closed file")
+        return self
+
+    def __exit__(self, exc, value, tb):
+        self._file.close()
+
     # file protocol
     def __iter__(self):
         return self._file.__iter__()

Lib/test/test_tempfile.py

@@ -1,5 +1,5 @@
 # tempfile.py unit tests.
-
+from __future__ import with_statement
 import tempfile
 import os
 import sys
@@ -619,7 +619,6 @@ class test_NamedTemporaryFile(TC):
 
     def test_multiple_close(self):
         # A NamedTemporaryFile can be closed many times without error
-
         f = tempfile.NamedTemporaryFile()
         f.write('abc\n')
         f.close()
@@ -629,6 +628,16 @@ class test_NamedTemporaryFile(TC):
         except:
             self.failOnException("close")
 
+    def test_context_manager(self):
+        # A NamedTemporaryFile can be used as a context manager
+        with tempfile.NamedTemporaryFile() as f:
+            self.failUnless(os.path.exists(f.name))
+        self.failIf(os.path.exists(f.name))
+        def use_closed():
+            with f:
+                pass
+        self.failUnlessRaises(ValueError, use_closed)
+
     # How to test the mode and bufsize parameters?
 
 test_classes.append(test_NamedTemporaryFile)
@@ -707,10 +716,23 @@ class test_SpooledTemporaryFile(TC):
         self.failUnless(f.fileno() > 0)
         self.failUnless(f._rolled)
 
-    def test_multiple_close(self):
+    def test_multiple_close_before_rollover(self):
         # A SpooledTemporaryFile can be closed many times without error
         f = tempfile.SpooledTemporaryFile()
         f.write('abc\n')
+        self.failIf(f._rolled)
+        f.close()
+        try:
+            f.close()
+            f.close()
+        except:
+            self.failOnException("close")
+
+    def test_multiple_close_after_rollover(self):
+        # A SpooledTemporaryFile can be closed many times without error
+        f = tempfile.SpooledTemporaryFile(max_size=1)
+        f.write('abc\n')
+        self.failUnless(f._rolled)
         f.close()
         try:
             f.close()
@@ -732,6 +754,46 @@ class test_SpooledTemporaryFile(TC):
         seek(0, 0)
         self.failUnless(read(70) == 'a'*35 + 'b'*35)
 
+    def test_context_manager_before_rollover(self):
+        # A SpooledTemporaryFile can be used as a context manager
+        with tempfile.SpooledTemporaryFile(max_size=1) as f:
+            self.failIf(f._rolled)
+            self.failIf(f.closed)
+        self.failUnless(f.closed)
+        def use_closed():
+            with f:
+                pass
+        self.failUnlessRaises(ValueError, use_closed)
+
+    def test_context_manager_during_rollover(self):
+        # A SpooledTemporaryFile can be used as a context manager
+        with tempfile.SpooledTemporaryFile(max_size=1) as f:
+            self.failIf(f._rolled)
+            f.write('abc\n')
+            f.flush()
+            self.failUnless(f._rolled)
+            self.failIf(f.closed)
+        self.failUnless(f.closed)
+        def use_closed():
+            with f:
+                pass
+        self.failUnlessRaises(ValueError, use_closed)
+
+    def test_context_manager_after_rollover(self):
+        # A SpooledTemporaryFile can be used as a context manager
+        f = tempfile.SpooledTemporaryFile(max_size=1)
+        f.write('abc\n')
+        f.flush()
+        self.failUnless(f._rolled)
+        with f:
+            self.failIf(f.closed)
+        self.failUnless(f.closed)
+        def use_closed():
+            with f:
+                pass
+        self.failUnlessRaises(ValueError, use_closed)
+
+
 test_classes.append(test_SpooledTemporaryFile)