gh-58451: Add optional delete_on_close parameter to NamedTemporaryFile

Doc/library/tempfile.rst

@@ -75,20 +75,61 @@ The module defines the following user-callable items:
  Added *errors* parameter.
 
 
-.. function:: NamedTemporaryFile(mode='w+b', buffering=-1, encoding=None, newline=None, suffix=None, prefix=None, dir=None, delete=True, *, errors=None)
-
- This function operates exactly as :func:`TemporaryFile` does, except that
- the file is guaranteed to have a visible name in the file system (on
- Unix, the directory entry is not unlinked). That name can be retrieved
- from the :attr:`name` attribute of the returned
- file-like object. Whether the name can be
- used to open the file a second time, while the named temporary file is
- still open, varies across platforms (it can be so used on Unix; it cannot
- on Windows). 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. This file-like object can
- be used in a :keyword:`with` statement, just like a normal file.
+.. function:: NamedTemporaryFile(mode='w+b', buffering=-1, encoding=None, newline=None, suffix=None, prefix=None, dir=None, delete=True, *, errors=None, delete_on_close=True)
+
+ This function operates exactly as :func:`TemporaryFile` does, except the
+ following differences:
+
+ * This function returns a file that is guaranteed to have a visible name in
+ the file system.
+ * To manage the named file, it extends the parameters of
+ :func:`TemporaryFile` with *delete* and *delete_on_close* parameters that
+ determine whether and how the named file should be automatically deleted.
+
+ The returned object is always a :term:`file-like object` whose :attr:`!file`
+ attribute is the underlying true file object. This :term:`file-like object`
+ can be used in a :keyword:`with` statement, just like a normal file. The
+ name of the temporary file can be retrieved from the :attr:`name` attribute
+ of the returned file-like object. On Unix, unlike with the
+ :func:`TemporaryFile`, the directory entry does not get unlinked immediately
+ after the file creation.
+
+ If *delete* is true (the default) and *delete_on_close* is true (the
+ default), the file is deleted as soon as it is closed. If *delete* is true
+ and *delete_on_close* is false, the file is deleted on context manager exit
+ only, or else when the :term:`file-like object` is finalized. Deletion is not
+ always guaranteed in this case (see :meth:`object.__del__`). If *delete* is
+ false, the value of *delete_on_close* is ignored.
+
+ Therefore to use the name of the temporary file to reopen the file after
+ closing it, either make sure not to delete the file upon closure (set the
+ *delete* parameter to be false) or, in case the temporary file is created in
+ a :keyword:`with` statement, set the *delete_on_close* parameter to be false.
+ The latter approach is recommended as it provides assistance in automatic
+ cleaning of the temporary file upon the context manager exit.
+
+ Opening the temporary file again by its name while it is still open works as
+ follows:
+
+ * On POSIX the file can always be opened again.
+ * On Windows, make sure that at least one of the following conditions are
+ fulfilled:
+
+ * *delete* is false
+ * additional open shares delete access (e.g. by calling :func:`os.open`
+ with the flag ``O_TEMPORARY``)
+ * *delete* is true but *delete_on_close* is false. Note, that in this
+ case the additional opens that do not share delete access (e.g.
+ created via builtin :func:`open`) must be closed before exiting the
+ context manager, else the :func:`os.unlink` call on context manager
+ exit will fail with a :exc:`PermissionError`.
+
+ On Windows, if *delete_on_close* is false, and the file is created in a
+ directory for which the user lacks delete access, then the :func:`os.unlink`
+ call on exit of the context manager will fail with a :exc:`PermissionError`.
+ This cannot happen when *delete_on_close* is true because delete access is
+ requested by the open, which fails immediately if the requested access is not
+ granted.
 
  On POSIX (only), a process that is terminated abruptly with SIGKILL
  cannot automatically delete any NamedTemporaryFiles it created.
@@ -98,6 +139,9 @@ The module defines the following user-callable items:
  .. versionchanged:: 3.8
  Added *errors* parameter.
 
+ .. versionchanged:: 3.12
+ Added *delete_on_close* parameter.
+
 
 .. class:: SpooledTemporaryFile(max_size=0, mode='w+b', buffering=-1, encoding=None, newline=None, suffix=None, prefix=None, dir=None, *, errors=None)
 
@@ -346,6 +390,19 @@ Here are some examples of typical usage of the :mod:`tempfile` module::
  >>>
  # file is now closed and removed
 
+ # create a temporary file using a context manager
+ # close the file, use the name to open the file again
+ >>> with tempfile.TemporaryFile(delete_on_close=False) as fp:
+ ... fp.write(b'Hello world!')
+ ... fp.close()
+ # the file is closed, but not removed
+ # open the file again by using its name
+ ... with open(fp.name) as f
+ ... f.read()
+ b'Hello world!'
+ >>>
+ # file is now removed
+
  # create a temporary directory using the context manager
  >>> with tempfile.TemporaryDirectory() as tmpdirname:
  ... print('created temporary directory', tmpdirname)

Doc/whatsnew/3.12.rst

@@ -142,6 +142,11 @@ unicodedata
 * The Unicode database has been updated to version 15.0.0. (Contributed by
  Benjamin Peterson in :gh:`96734`).
 
+tempfile
+--------
+
+The :class:`tempfile.NamedTemporaryFile` function has a new optional parameter
+*delete_on_close* (Contributed by Evgeny Zorin in :gh:`58451`.)
 
 Optimizations
 =============

Lib/tempfile.py

@@ -418,42 +418,42 @@ class _TemporaryFileCloser:
  underlying file object, without adding a __del__ method to the
  temporary file."""
 
-file = None # Set here since __del__ checks it
+cleanup_called = False
  close_called = False
 
- def __init__(self, file, name, delete=True):
+ def __init__(self, file, name, delete=True, delete_on_close=True):
  self.file = file
  self.name = name
  self.delete = delete
+ self.delete_on_close = delete_on_close
 
- # 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
- # name TemporaryFileWrapper may also get None'd out before
- # __del__ is called.
-
- def close(self, unlink=_os.unlink):
- if not self.close_called and self.file is not None:
- self.close_called = True
- try:
+ def cleanup(self, windows=(_os.name == 'nt'), unlink=_os.unlink):
+ if not self.cleanup_called:
+ self.cleanup_called = True
+ try:
+ if not self.close_called:
+ self.close_called = True
  self.file.close()
- finally:
- if self.delete:
+ finally:
+ # Windows provides delete-on-close as a primitive, in which
+ # case the file was deleted by self.file.close().
+ if self.delete and not (windows and self.delete_on_close):
+ try:
  unlink(self.name)
+ except FileNotFoundError:
+ pass
 
- # Need to ensure the file is deleted on __del__
- def __del__(self):
- self.close()
-
- else:
- def close(self):
- if not self.close_called:
- self.close_called = True
+ def close(self):
+ if not self.close_called:
+ self.close_called = True
+ try:
  self.file.close()
+ finally:
+ if self.delete and self.delete_on_close:
+ self.cleanup()
+
+ def __del__(self):
+ self.cleanup()
 
 
 class _TemporaryFileWrapper:
@@ -464,11 +464,11 @@ class _TemporaryFileWrapper:
  remove the file when it is no longer needed.
  """
 
- def __init__(self, file, name, delete=True):
+ def __init__(self, file, name, delete=True, delete_on_close=True):
  self.file = file
  self.name = name
- self.delete = delete
-self._closer = _TemporaryFileCloser(file, name, delete)
+ self._closer = _TemporaryFileCloser(file, name, delete,
+ delete_on_close)
 
  def __getattr__(self, name):
  # Attribute lookups are delegated to the underlying file
@@ -499,7 +499,7 @@ def __enter__(self):
  # deleted when used in a with statement
  def __exit__(self, exc, value, tb):
  result = self.file.__exit__(exc, value, tb)
- self.close()
+ self._closer.cleanup()
  return result
 
  def close(self):
@@ -518,18 +518,21 @@ def __iter__(self):
  for line in self.file:
  yield line
 
-
 def NamedTemporaryFile(mode='w+b', buffering=-1, encoding=None,
  newline=None, suffix=None, prefix=None,
- dir=None, delete=True, *, errors=None):
+ dir=None, delete=True, *, errors=None,
+ delete_on_close=True):
  """Create and return a temporary file.
  Arguments:
  'prefix', 'suffix', 'dir' -- as for mkstemp.
  'mode' -- the mode argument to io.open (default "w+b").
  'buffering' -- the buffer size argument to io.open (default -1).
  'encoding' -- the encoding argument to io.open (default None)
  'newline' -- the newline argument to io.open (default None)
- 'delete' -- whether the file is deleted on close (default True).
+ 'delete' -- whether the file is automatically deleted (default True).
+ 'delete_on_close' -- if 'delete', whether the file is deleted on close
+ (default True) or otherwise either on context manager exit
+ (if context manager was used) or on object finalization. .
  'errors' -- the errors argument to io.open (default None)
  The file is created as mkstemp() would do it.
 
@@ -548,7 +551,7 @@ def NamedTemporaryFile(mode='w+b', buffering=-1, encoding=None,
 
  # Setting O_TEMPORARY in the flags causes the OS to delete
  # the file when it is closed. This is only supported by Windows.
- if _os.name == 'nt' and delete:
+ if _os.name == 'nt' and delete and delete_on_close:
  flags |= _os.O_TEMPORARY
 
  if "b" not in mode:
@@ -567,12 +570,13 @@ def opener(*args):
  raw = getattr(file, 'buffer', file)
  raw = getattr(raw, 'raw', raw)
  raw.name = name
- return _TemporaryFileWrapper(file, name, delete)
+ return _TemporaryFileWrapper(file, name, delete, delete_on_close)
  except:
  file.close()
  raise
  except:
- if name is not None and not (_os.name == 'nt' and delete):
+ if name is not None and not (
+ _os.name == 'nt' and delete and delete_on_close):
  _os.unlink(name)
  raise
 

Lib/test/test_tempfile.py

@@ -11,6 +11,7 @@
 import stat
 import types
 import weakref
+import gc
 from unittest import mock
 
 import unittest
@@ -1013,6 +1014,102 @@ def use_closed():
  pass
  self.assertRaises(ValueError, use_closed)
 
+ def test_context_man_not_del_on_close_if_delete_on_close_false(self):
+ # Issue gh-58451: tempfile.NamedTemporaryFile is not particulary useful
+ # on Windows
+ # A NamedTemporaryFile is NOT deleted when closed if
+ # delete_on_close=False, but is deleted on context manager exit
+ dir = tempfile.mkdtemp()
+ try:
+ with tempfile.NamedTemporaryFile(dir=dir,
+ delete=True,
+ delete_on_close=False) as f:
+ f.write(b'blat')
+ f_name = f.name
+ f.close()
+ with self.subTest():
+ # Testing that file is not deleted on close
+ self.assertTrue(os.path.exists(f.name),
+ f"NamedTemporaryFile {f.name!r} is incorrectly "
+ f"deleted on closure when delete_on_close=False")
+
+ with self.subTest():
+ # Testing that file is deleted on context manager exit
+ self.assertFalse(os.path.exists(f.name),
+ f"NamedTemporaryFile {f.name!r} exists "
+ f"after context manager exit")
+
+ finally:
+ os.rmdir(dir)
+
+ def test_context_man_ok_to_delete_manually(self):
+ # In the case of delete=True, a NamedTemporaryFile can be manually
+ # deleted in a with-statement context without causing an error.
+ dir = tempfile.mkdtemp()
+ try:
+ with tempfile.NamedTemporaryFile(dir=dir,
+ delete=True,
+ delete_on_close=False) as f:
+ f.write(b'blat')
+ f.close()
+ os.unlink(f.name)
+
+ finally:
+ os.rmdir(dir)
+
+ def test_context_man_not_del_if_delete_false(self):
+ # A NamedTemporaryFile is not deleted if delete = False
+ dir = tempfile.mkdtemp()
+ f_name = ""
+ try:
+ # Test that delete_on_close=True has no effect if delete=False.
+ with tempfile.NamedTemporaryFile(dir=dir, delete=False,
+ delete_on_close=True) as f:
+ f.write(b'blat')
+ f_name = f.name
+ self.assertTrue(os.path.exists(f.name),
+ f"NamedTemporaryFile {f.name!r} exists after close")
+ finally:
+ os.unlink(f_name)
+ os.rmdir(dir)
+
+ def test_del_by_finalizer(self):
+ # A NamedTemporaryFile is deleted when finalized in the case of
+ # delete=True, delete_on_close=False, and no with-statement is used.
+ def my_func(dir):
+ f = tempfile.NamedTemporaryFile(dir=dir, delete=True,
+ delete_on_close=False)
+ tmp_name = f.name
+ f.write(b'blat')
+ # Testing extreme case, where the file is not explicitly closed
+ # f.close()
+ return tmp_name
+ # Make sure that the garbage collector has finalized the file object.
+ gc.collect()
+ dir = tempfile.mkdtemp()
+ try:
+ tmp_name = my_func(dir)
+ self.assertFalse(os.path.exists(tmp_name),
+ f"NamedTemporaryFile {tmp_name!r} "
+ f"exists after finalizer ")
+ finally:
+ os.rmdir(dir)
+
+ def test_correct_finalizer_work_if_already_deleted(self):
+ # There should be no error in the case of delete=True,
+ # delete_on_close=False, no with-statement is used, and the file is
+ # deleted manually.
+ def my_func(dir)->str:
+ f = tempfile.NamedTemporaryFile(dir=dir, delete=True,
+ delete_on_close=False)
+ tmp_name = f.name
+ f.write(b'blat')
+ f.close()
+ os.unlink(tmp_name)
+ return tmp_name
+ # Make sure that the garbage collector has finalized the file object.
+ gc.collect()
+
  def test_bad_mode(self):
  dir = tempfile.mkdtemp()
  self.addCleanup(os_helper.rmtree, dir)
@@ -1081,7 +1178,8 @@ def test_iobase_interface(self):
  missing_attrs = iobase_attrs - spooledtempfile_attrs
  self.assertFalse(
  missing_attrs,
- 'SpooledTemporaryFile missing attributes from IOBase/BufferedIOBase/TextIOBase'
+ 'SpooledTemporaryFile missing attributes from '
+ 'IOBase/BufferedIOBase/TextIOBase'
  )
 
  def test_del_on_close(self):

Misc/NEWS.d/next/Library/2020-09-28-04-56-04.bpo-14243.YECnxv.rst

@@ -0,0 +1 @@
+The :class:`tempfile.NamedTemporaryFile` function has a new optional parameter *delete_on_close*