tempfile.rst

:mod:`tempfile` --- Generate temporary files and directories
============================================================

.. sectionauthor:: Zack Weinberg <zack@codesourcery.com>


.. module:: tempfile
   :synopsis: Generate temporary files and directories.


.. index::
   pair: temporary; file name
   pair: temporary; file

**Source code:** :source:`Lib/tempfile.py`

--------------

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.
To maintain backward compatibility, the argument order is somewhat odd; it
is recommended to use keyword arguments for clarity.

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
   as it is closed (including an implicit close when the object is garbage
   collected).  Under Unix, the directory entry for the file 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 *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 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.


.. function:: NamedTemporaryFile(mode='w+b', buffering=None, encoding=None, newline=None, suffix='', prefix='tmp', dir=None, delete=True)

   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 file 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 NT or later).  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:: SpooledTemporaryFile(max_size=0, mode='w+b', buffering=None, encoding=None, newline=None, suffix='', prefix='tmp', dir=None)

   This function operates exactly as :func:`TemporaryFile` does, except that
   data is spooled in memory until the file size exceeds *max_size*, or
   until the file's :func:`fileno` method is called, at which point the
   contents are written to disk and operation proceeds as with
   :func:`TemporaryFile`.

   The resulting file has one additional method, :func:`rollover`, which
   causes the file to roll over to an on-disk file regardless of its size.

   The returned object is a file-like object whose :attr:`_file` attribute
   is either a :class:`io.BytesIO` or :class:`io.StringIO` object (depending on
   whether binary or text *mode* was specified) or a true file
   object, depending on whether :func:`rollover` has been called.  This
   file-like object can be used in a :keyword:`with` statement, just like
   a normal file.

   .. versionchanged:: 3.3
      the truncate method now accepts a ``size`` argument.


.. 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).
   The resulting object can be used as a context manager (see
   :ref:`context-managers`).  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.

   The directory name can be retrieved from the :attr:`name` attribute of the
   returned object.  When the returned object is used as a context manager, the
   :attr:`name` will be assigned to the target of the :keyword:`as` clause in
   the :keyword:`with` statement, if there is one.

   The directory can be explicitly cleaned up by calling the
   :func:`cleanup` method.

   .. versionadded:: 3.2


.. function:: mkstemp(suffix='', prefix='tmp', dir=None, text=False)

   Creates a temporary file in the most secure manner possible.  There are
   no race conditions in the file's creation, assuming that the platform
   properly implements the :const:`os.O_EXCL` flag for :func:`os.open`.  The
   file is readable and writable only by the creating user ID.  If the
   platform uses permission bits to indicate whether a file is executable,
   the file is executable by no one.  The file descriptor is not inherited
   by child processes.

   Unlike :func:`TemporaryFile`, the user of :func:`mkstemp` is responsible
   for deleting the temporary file when done with it.

   If *suffix* is specified, the file name will end with that suffix,
   otherwise there will be no suffix.  :func:`mkstemp` does not put a dot
   between the file name and the suffix; if you need one, put it at the
   beginning of *suffix*.

   If *prefix* is specified, the file name will begin with that prefix;
   otherwise, a default prefix is used.

   If *dir* is specified, the file will be created in that directory;
   otherwise, a default directory is used.  The default directory is chosen
   from a platform-dependent list, but the user of the application can
   control the directory location by setting the *TMPDIR*, *TEMP* or *TMP*
   environment variables.  There is thus no guarantee that the generated
   filename will have any nice properties, such as not requiring quoting
   when passed to external commands via ``os.popen()``.

   If *text* is specified, it indicates whether to open the file in binary
   mode (the default) or text mode.  On some platforms, this makes no
   difference.

   :func:`mkstemp` returns a tuple containing an OS-level handle to an open
   file (as would be returned by :func:`os.open`) and the absolute pathname
   of that file, in that order.


.. function:: mkdtemp(suffix='', prefix='tmp', dir=None)

   Creates a temporary directory in the most secure manner possible. There
   are no race conditions in the directory's creation.  The directory is
   readable, writable, and searchable only by the creating user ID.

   The user of :func:`mkdtemp` is responsible for deleting the temporary
   directory and its contents when done with it.

   The *prefix*, *suffix*, and *dir* arguments are the same as for
   :func:`mkstemp`.

   :func:`mkdtemp` returns the absolute pathname of the new directory.


.. 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 two global variables 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.


.. 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, 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:

   #. The directory named by the :envvar:`TMPDIR` environment variable.

   #. The directory named by the :envvar:`TEMP` environment variable.

   #. The directory named by the :envvar:`TMP` environment variable.

   #. A platform-specific location:

      * On Windows, the directories :file:`C:\\TEMP`, :file:`C:\\TMP`,
        :file:`\\TEMP`, and :file:`\\TMP`, in that order.

      * On all other platforms, the directories :file:`/tmp`, :file:`/var/tmp`, and
        :file:`/usr/tmp`, in that order.

   #. 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.


.. function:: gettempprefix()

   Return the filename prefix used to create temporary files.  This does not
   contain the directory component.


Examples
--------

Here are some examples of typical usage of the :mod:`tempfile` module::

    >>> import tempfile

    # create a temporary file and write some data to it
    >>> fp = tempfile.TemporaryFile()
    >>> fp.write(b'Hello world!')
    # read data from file
    >>> fp.seek(0)
    >>> fp.read()
    b'Hello world!'
    # close the file, it will be removed
    >>> fp.close()

    # create a temporary file using a context manager
    >>> with tempfile.TemporaryFile() as fp:
    ...     fp.write(b'Hello world!')
    ...     fp.seek(0)
    ...     fp.read()
    b'Hello world!'
    >>>
    # file is now closed and removed

    # create a temporary directory using the context manager
    >>> with tempfile.TemporaryDirectory() as tmpdirname:
    ...     print('created temporary directory', tmpdirname)
    >>>
    # directory and contents have been removed