Issue 2021: Allow NamedTemporaryFile and SpooledTemporaryFile to be used as context managers. (The NamedTemporaryFile fix should be considered for backporting to 2.5)
diff --git a/Doc/library/tempfile.rst b/Doc/library/tempfile.rst
index ae1c610..2f37ede 100644
--- a/Doc/library/tempfile.rst
+++ b/Doc/library/tempfile.rst
@@ -51,7 +51,8 @@
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 @@
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 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
diff --git a/Lib/tempfile.py b/Lib/tempfile.py
index c0e34bc..e75c8fe 100644
--- a/Lib/tempfile.py
+++ b/Lib/tempfile.py
@@ -370,6 +370,7 @@
raise IOError, (_errno.EEXIST, "No usable temporary filename found")
+
class _TemporaryFileWrapper:
"""Temporary file wrapper
@@ -385,17 +386,25 @@
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 @@
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 @@
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__()
diff --git a/Lib/test/test_tempfile.py b/Lib/test/test_tempfile.py
index 96e6591..a44be26 100644
--- a/Lib/test/test_tempfile.py
+++ b/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 @@
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 @@
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 @@
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 @@
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)