Issue #23725: Overhaul tempfile docs.

Patch from Zbigniew Jędrzejewski-Szmek.

1 files changed, 89 insertions, 66 deletions

diff --git a/Doc/library/tempfile.rst b/Doc/library/tempfile.rst
index 0387fb1..83f9941 100644
--- a/Doc/library/tempfile.rst
+++ b/Doc/library/tempfile.rst
@@ -16,16 +16,18 @@
 
 --------------
 
-This module generates temporary files and directories.  It works on all
-supported platforms.  It provides three new functions,
-:func:`NamedTemporaryFile`, :func:`mkstemp`, and :func:`mkdtemp`, which should
-eliminate all remaining need to use the insecure :func:`mktemp` function.
-Temporary file names created by this module no longer contain the process ID;
-instead a string of six random characters is used.
-
-Also, all the user-callable functions now take additional arguments which
-allow direct control over the location and name of temporary files.  It is
-no longer necessary to use the global *tempdir* variable.
+This module creates temporary files and directories.  It works on all
+supported platforms. :class:`TemporaryFile`, :class:`NamedTemporaryFile`,
+:class:`TemporaryDirectory`, and :class:`SpooledTemporaryFile` are high-level
+interfaces which provide automatic cleanup and can be used as
+context managers. :func:`mkstemp` and
+:func:`mkdtemp` are lower-level functions which require manual cleanup.
+
+All the user-callable functions and constructors take additional arguments which
+allow direct control over the location and name of temporary files and
+directories. Files names used by this module include a string of
+random characters which allows those files to be securely created in
+shared temporary directories.
 To maintain backward compatibility, the argument order is somewhat odd; it
 is recommended to use keyword arguments for clarity.
 
@@ -34,28 +36,33 @@ The module defines the following user-callable items:
 .. function:: TemporaryFile(mode='w+b', buffering=None, encoding=None, newline=None, suffix='', prefix='tmp', dir=None)
 
    Return a :term:`file-like object` that can be used as a temporary storage area.
-   The file is created using :func:`mkstemp`. It will be destroyed as soon
+   The file is created securely, using the same rules as :func:`mkstemp`. It will be destroyed as soon
    as it is closed (including an implicit close when the object is garbage
-   collected).  Under Unix, the directory entry for the file is removed
+   collected).  Under Unix, the directory entry for the file is either not created at all or is removed
    immediately after the file is created.  Other platforms do not support
    this; your code should not rely on a temporary file created using this
    function having or not having a visible name in the file system.
 
+   The resulting object can be used as a context manager (see
+   :ref:`tempfile-examples`).  On completion of the context or
+   destruction of the file object the temporary file will be removed
+   from the filesystem.
+
    The *mode* parameter defaults to ``'w+b'`` so that the file created can
    be read and written without being closed.  Binary mode is used so that it
    behaves consistently on all platforms without regard for the data that is
    stored.  *buffering*, *encoding* and *newline* are interpreted as for
    :func:`open`.
 
-   The *dir*, *prefix* and *suffix* parameters are passed to :func:`mkstemp`.
+   The *dir*, *prefix* and *suffix* parameters have the same meaning
+   as with :func:`mkstemp`.
 
    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. This file-like object can be used in a
-   :keyword:`with` statement, just like a normal file.
+   underlying true file object.
 
    The :py:data:`os.O_TMPFILE` flag is used if it is available and works
-   (Linux-specific, require Linux kernel 3.11 or later).
+   (Linux-specific, requires Linux kernel 3.11 or later).
 
    .. versionchanged:: 3.5
 
@@ -101,10 +108,9 @@ The module defines the following user-callable items:
 
 .. function:: TemporaryDirectory(suffix='', prefix='tmp', dir=None)
 
-   This function creates a temporary directory using :func:`mkdtemp`
-   (the supplied arguments are passed directly to the underlying function).
+   This function securely creates a temporary directory using the same rules as :func:`mkdtemp`.
    The resulting object can be used as a context manager (see
-   :ref:`context-managers`).  On completion of the context or destruction
+   :ref:`tempfile-examples`).  On completion of the context or destruction
    of the temporary directory object the newly created temporary directory
    and all its contents are removed from the filesystem.
 
@@ -194,49 +200,14 @@ The module defines the following user-callable items:
       an appropriate default value to be used.
 
 
-.. function:: mktemp(suffix='', prefix='tmp', dir=None)
-
-   .. deprecated:: 2.3
-      Use :func:`mkstemp` instead.
-
-   Return an absolute pathname of a file that did not exist at the time the
-   call is made.  The *prefix*, *suffix*, and *dir* arguments are the same
-   as for :func:`mkstemp`.
-
-   .. warning::
-
-      Use of this function may introduce a security hole in your program.  By
-      the time you get around to doing anything with the file name it returns,
-      someone else may have beaten you to the punch.  :func:`mktemp` usage can
-      be replaced easily with :func:`NamedTemporaryFile`, passing it the
-      ``delete=False`` parameter::
-
-         >>> f = NamedTemporaryFile(delete=False)
-         >>> f.name
-         '/tmp/tmptjujjt'
-         >>> f.write(b"Hello World!\n")
-         13
-         >>> f.close()
-         >>> os.unlink(f.name)
-         >>> os.path.exists(f.name)
-         False
-
-The module uses a global variable that tell it how to construct a
-temporary name.  They are initialized at the first call to any of the
-functions above.  The caller may change them, but this is discouraged; use
-the appropriate function arguments, instead.
-
+.. function:: gettempdir()
 
-.. data:: tempdir
+   Return the name of the directory used for temporary files. This
+   defines the default value for the *dir* argument to all functions
+   in this module.
 
-   When set to a value other than ``None``, this variable defines the
-   default value for the *dir* argument to all the functions defined in this
-   module.
-
-   If ``tempdir`` is unset or ``None`` at any call to any of the above
-   functions, Python searches a standard list of directories and sets
-   *tempdir* to the first one which the calling user can create files in.
-   The list is:
+   Python searches a standard list of directories to find one which
+   the calling user can create files in.  The list is:
 
    #. The directory named by the :envvar:`TMPDIR` environment variable.
 
@@ -254,12 +225,8 @@ the appropriate function arguments, instead.
 
    #. As a last resort, the current working directory.
 
-
-.. function:: gettempdir()
-
-   Return the directory currently selected to create temporary files in. If
-   :data:`tempdir` is not ``None``, this simply returns its contents; otherwise,
-   the search described above is performed, and the result returned.
+   The result of this search is cached, see the description of
+   :data:`tempdir` below.
 
 .. function:: gettempdirb()
 
@@ -278,6 +245,23 @@ the appropriate function arguments, instead.
 
    .. versionadded:: 3.5
 
+The module uses a global variable to store the name of the directory
+used for temporary files returned by :func:`gettempdir`.  It can be
+set directly to override the selection process, but this is discouraged.
+All functions in this module take a *dir* argument which can be used
+to specify the directory and this is the recommend approach.
+
+.. data:: tempdir
+
+   When set to a value other than ``None``, this variable defines the
+   default value for the *dir* argument to all the functions defined in this
+   module.
+
+   If ``tempdir`` is unset or ``None`` at any call to any of the above
+   functions except :func:`gettempprefix` it is initalized following the
+   algorithm described in :func:`gettempdir`.
+
+.. _tempfile-examples:
 
 Examples
 --------
@@ -311,3 +295,42 @@ Here are some examples of typical usage of the :mod:`tempfile` module::
     >>>
     # directory and contents have been removed
 
+
+Deprecated functions and variables
+----------------------------------
+
+A historical way to create temporary files was to first generate a
+file name with the :func:`mktemp` function and then create a file
+using this name. Unfortunately this is not secure, because a different
+process may create a file with this name in the time between the call
+to :func:`mktemp` and the subsequent attempt to create the file by the
+first process. The solution is to combine the two steps and create the
+file immediately. This approach is used by :func:`mkstemp` and the
+other functions described above.
+
+.. function:: mktemp(suffix='', prefix='tmp', dir=None)
+
+   .. deprecated:: 2.3
+      Use :func:`mkstemp` instead.
+
+   Return an absolute pathname of a file that did not exist at the time the
+   call is made.  The *prefix*, *suffix*, and *dir* arguments are the same
+   as for :func:`mkstemp`.
+
+   .. warning::
+
+      Use of this function may introduce a security hole in your program.  By
+      the time you get around to doing anything with the file name it returns,
+      someone else may have beaten you to the punch.  :func:`mktemp` usage can
+      be replaced easily with :func:`NamedTemporaryFile`, passing it the
+      ``delete=False`` parameter::
+
+         >>> f = NamedTemporaryFile(delete=False)
+         >>> f.name
+         '/tmp/tmptjujjt'
+         >>> f.write(b"Hello World!\n")
+         13
+         >>> f.close()
+         >>> os.unlink(f.name)
+         >>> os.path.exists(f.name)
+         False