11.6. "tempfile" — Generate temporary files and directories
***********************************************************

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

======================================================================

This module creates temporary files and directories.  It works on all
supported platforms. "TemporaryFile", "NamedTemporaryFile",
"TemporaryDirectory", and "SpooledTemporaryFile" are high-level
interfaces which provide automatic cleanup and can be used as context
managers. "mkstemp()" and "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.

The module defines the following user-callable items:

tempfile.TemporaryFile(mode='w+b', buffering=None, encoding=None, newline=None, suffix=None, prefix=None, dir=None)

   Return a *file-like object* that can be used as a temporary storage
   area. The file is created securely, using the same rules as
   "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 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
   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 "open()".

   The *dir*, *prefix* and *suffix* parameters have the same meaning
   and defaults as with "mkstemp()".

   The returned object is a true file object on POSIX platforms.  On
   other platforms, it is a file-like object whose "file" attribute is
   the underlying true file object.

   The "os.O_TMPFILE" flag is used if it is available and works
   (Linux-specific, requires Linux kernel 3.11 or later).

   Changed in version 3.5: The "os.O_TMPFILE" flag is now used if
   available.

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

   This function operates exactly as "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 "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
   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 "file" attribute is the underlying true file
   object. This file-like object can be used in a "with" statement,
   just like a normal file.

tempfile.SpooledTemporaryFile(max_size=0, mode='w+b', buffering=None, encoding=None, newline=None, suffix=None, prefix=None, dir=None)

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

   The resulting file has one additional method, "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 "_file" attribute
   is either an "io.BytesIO" or "io.StringIO" object (depending on
   whether binary or text *mode* was specified) or a true file object,
   depending on whether "rollover()" has been called.  This file-like
   object can be used in a "with" statement, just like a normal file.

   Changed in version 3.3: the truncate method now accepts a "size"
   argument.

tempfile.TemporaryDirectory(suffix=None, prefix=None, dir=None)

   This function securely creates a temporary directory using the same
   rules as "mkdtemp()". The resulting object can be used as a context
   manager (see 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.

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

   The directory can be explicitly cleaned up by calling the
   "cleanup()" method.

   New in version 3.2.

tempfile.mkstemp(suffix=None, prefix=None, 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 "os.O_EXCL" flag for "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 "TemporaryFile()", the user of "mkstemp()" is responsible
   for deleting the temporary file when done with it.

   If *suffix* is not "None", the file name will end with that suffix,
   otherwise there will be no suffix.  "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 not "None", the file name will begin with that
   prefix; otherwise, a default prefix is used.  The default is the
   return value of "gettempprefix()" or "gettempprefixb()", as
   appropriate.

   If *dir* is not "None", 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 any of *suffix*, *prefix*, and *dir* are not "None", they must
   be the same type. If they are bytes, the returned name will be
   bytes instead of str. If you want to force a bytes return value
   with otherwise default behavior, pass "suffix=b''".

   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.

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

   Changed in version 3.5: *suffix*, *prefix*, and *dir* may now be
   supplied in bytes in order to obtain a bytes return value.  Prior
   to this, only str was allowed. *suffix* and *prefix* now accept and
   default to "None" to cause an appropriate default value to be used.

tempfile.mkdtemp(suffix=None, prefix=None, 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 "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
   "mkstemp()".

   "mkdtemp()" returns the absolute pathname of the new directory.

   Changed in version 3.5: *suffix*, *prefix*, and *dir* may now be
   supplied in bytes in order to obtain a bytes return value.  Prior
   to this, only str was allowed. *suffix* and *prefix* now accept and
   default to "None" to cause an appropriate default value to be used.

tempfile.gettempdir()

   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.

   Python searches a standard list of directories to find one which
   the calling user can create files in.  The list is:

   1. The directory named by the "TMPDIR" environment variable.

   2. The directory named by the "TEMP" environment variable.

   3. The directory named by the "TMP" environment variable.

   4. A platform-specific location:

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

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

   5. As a last resort, the current working directory.

   The result of this search is cached, see the description of
   "tempdir" below.

tempfile.gettempdirb()

   Same as "gettempdir()" but the return value is in bytes.

   New in version 3.5.

tempfile.gettempprefix()

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

tempfile.gettempprefixb()

   Same as "gettempprefix()" but the return value is in bytes.

   New in version 3.5.

The module uses a global variable to store the name of the directory
used for temporary files returned by "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 recommended approach.

tempfile.tempdir

   When set to a value other than "None", this variable defines the
   default value for the *dir* argument to the functions defined in
   this module.

   If "tempdir" is unset or "None" at any call to any of the above
   functions except "gettempprefix()" it is initialized following the
   algorithm described in "gettempdir()".


11.6.1. Examples
================

Here are some examples of typical usage of the "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


11.6.2. Deprecated functions and variables
==========================================

A historical way to create temporary files was to first generate a
file name with the "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 "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 "mkstemp()" and the other
functions described above.

tempfile.mktemp(suffix='', prefix='tmp', dir=None)

   Deprecated since version 2.3: Use "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 similar to those of "mkstemp()", except that bytes file names,
   "suffix=None" and "prefix=None" are not supported.

   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.  "mktemp()" usage can be replaced easily with
     "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
