gh-58451: Add optional delete_on_close parameter to NamedTemporaryFile

Doc/library/tempfile.rst

@@ -75,20 +75,58 @@ 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:
+
+   * The file is guaranteed to have a visible name in the file system
+     (on Unix, the directory entry is not unlinked).
+   * There is more granularity in the deletion behaviour of the file
+     (see *delete_on_close* below)
+
+   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.
+
+   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 open the closed file
+   second time, 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 to open the file again while it is open 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 +136,9 @@ 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 +387,19 @@ 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*