/Doc/library/tempfile.rst

  1
  2:mod:`tempfile` --- Generate temporary files and directories
  3============================================================
  4
  5.. sectionauthor:: Zack Weinberg <zack@codesourcery.com>
  6
  7
  8.. module:: tempfile
  9   :synopsis: Generate temporary files and directories.
 10
 11
 12.. index::
 13   pair: temporary; file name
 14   pair: temporary; file
 15
 16This module generates temporary files and directories.  It works on all
 17supported platforms.
 18
 19In version 2.3 of Python, this module was overhauled for enhanced security.  It
 20now provides three new functions, :func:`NamedTemporaryFile`, :func:`mkstemp`,
 21and :func:`mkdtemp`, which should eliminate all remaining need to use the
 22insecure :func:`mktemp` function.  Temporary file names created by this module
 23no longer contain the process ID; instead a string of six random characters is
 24used.
 25
 26Also, all the user-callable functions now take additional arguments which
 27allow direct control over the location and name of temporary files.  It is
 28no longer necessary to use the global *tempdir* and *template* variables.
 29To maintain backward compatibility, the argument order is somewhat odd; it
 30is recommended to use keyword arguments for clarity.
 31
 32The module defines the following user-callable functions:
 33
 34
 35.. function:: TemporaryFile([mode='w+b'[, bufsize=-1[, suffix=''[, prefix='tmp'[, dir=None]]]]])
 36
 37   Return a file-like object that can be used as a temporary storage area.
 38   The file is created using :func:`mkstemp`. It will be destroyed as soon
 39   as it is closed (including an implicit close when the object is garbage
 40   collected).  Under Unix, the directory entry for the file is removed
 41   immediately after the file is created.  Other platforms do not support
 42   this; your code should not rely on a temporary file created using this
 43   function having or not having a visible name in the file system.
 44
 45   The *mode* parameter defaults to ``'w+b'`` so that the file created can
 46   be read and written without being closed.  Binary mode is used so that it
 47   behaves consistently on all platforms without regard for the data that is
 48   stored.  *bufsize* defaults to ``-1``, meaning that the operating system
 49   default is used.
 50
 51   The *dir*, *prefix* and *suffix* parameters are passed to :func:`mkstemp`.
 52
 53   The returned object is a true file object on POSIX platforms.  On other
 54   platforms, it is a file-like object whose :attr:`file` attribute is the
 55   underlying true file object. This file-like object can be used in a
 56   :keyword:`with` statement, just like a normal file.
 57
 58
 59.. function:: NamedTemporaryFile([mode='w+b'[, bufsize=-1[, suffix=''[, prefix='tmp'[, dir=None[, delete=True]]]]]])
 60
 61   This function operates exactly as :func:`TemporaryFile` does, except that
 62   the file is guaranteed to have a visible name in the file system (on
 63   Unix, the directory entry is not unlinked).  That name can be retrieved
 64   from the :attr:`name` member of the file object.  Whether the name can be
 65   used to open the file a second time, while the named temporary file is
 66   still open, varies across platforms (it can be so used on Unix; it cannot
 67   on Windows NT or later).  If *delete* is true (the default), the file is
 68   deleted as soon as it is closed.
 69
 70   The returned object is always a file-like object whose :attr:`file`
 71   attribute is the underlying true file object. This file-like object can
 72   be used in a :keyword:`with` statement, just like a normal file.
 73
 74   .. versionadded:: 2.3
 75
 76   .. versionadded:: 2.6
 77      The *delete* parameter.
 78
 79
 80.. function:: SpooledTemporaryFile([max_size=0, [mode='w+b'[, bufsize=-1[, suffix=''[, prefix='tmp'[, dir=None]]]]]])
 81
 82   This function operates exactly as :func:`TemporaryFile` does, except that
 83   data is spooled in memory until the file size exceeds *max_size*, or
 84   until the file's :func:`fileno` method is called, at which point the
 85   contents are written to disk and operation proceeds as with
 86   :func:`TemporaryFile`.
 87
 88   The resulting file has one additional method, :func:`rollover`, which
 89   causes the file to roll over to an on-disk file regardless of its size.
 90
 91   The returned object is a file-like object whose :attr:`_file` attribute
 92   is either a :class:`StringIO` object or a true file object, depending on
 93   whether :func:`rollover` has been called. This file-like object can be
 94   used in a :keyword:`with` statement, just like a normal file.
 95
 96   .. versionadded:: 2.6
 97
 98
 99.. function:: mkstemp([suffix=''[, prefix='tmp'[, dir=None[, text=False]]]])
100
101   Creates a temporary file in the most secure manner possible.  There are
102   no race conditions in the file's creation, assuming that the platform
103   properly implements the :const:`os.O_EXCL` flag for :func:`os.open`.  The
104   file is readable and writable only by the creating user ID.  If the
105   platform uses permission bits to indicate whether a file is executable,
106   the file is executable by no one.  The file descriptor is not inherited
107   by child processes.
108
109   Unlike :func:`TemporaryFile`, the user of :func:`mkstemp` is responsible
110   for deleting the temporary file when done with it.
111
112   If *suffix* is specified, the file name will end with that suffix,
113   otherwise there will be no suffix.  :func:`mkstemp` does not put a dot
114   between the file name and the suffix; if you need one, put it at the
115   beginning of *suffix*.
116
117   If *prefix* is specified, the file name will begin with that prefix;
118   otherwise, a default prefix is used.
119
120   If *dir* is specified, the file will be created in that directory;
121   otherwise, a default directory is used.  The default directory is chosen
122   from a platform-dependent list, but the user of the application can
123   control the directory location by setting the *TMPDIR*, *TEMP* or *TMP*
124   environment variables.  There is thus no guarantee that the generated
125   filename will have any nice properties, such as not requiring quoting
126   when passed to external commands via ``os.popen()``.
127
128   If *text* is specified, it indicates whether to open the file in binary
129   mode (the default) or text mode.  On some platforms, this makes no
130   difference.
131
132   :func:`mkstemp` returns a tuple containing an OS-level handle to an open
133   file (as would be returned by :func:`os.open`) and the absolute pathname
134   of that file, in that order.
135
136   .. versionadded:: 2.3
137
138
139.. function:: mkdtemp([suffix=''[, prefix='tmp'[, dir=None]]])
140
141   Creates a temporary directory in the most secure manner possible. There
142   are no race conditions in the directory's creation.  The directory is
143   readable, writable, and searchable only by the creating user ID.
144
145   The user of :func:`mkdtemp` is responsible for deleting the temporary
146   directory and its contents when done with it.
147
148   The *prefix*, *suffix*, and *dir* arguments are the same as for
149   :func:`mkstemp`.
150
151   :func:`mkdtemp` returns the absolute pathname of the new directory.
152
153   .. versionadded:: 2.3
154
155
156.. function:: mktemp([suffix=''[, prefix='tmp'[, dir=None]]])
157
158   .. deprecated:: 2.3
159      Use :func:`mkstemp` instead.
160
161   Return an absolute pathname of a file that did not exist at the time the
162   call is made.  The *prefix*, *suffix*, and *dir* arguments are the same
163   as for :func:`mkstemp`.
164
165   .. warning::
166
167      Use of this function may introduce a security hole in your program.  By
168      the time you get around to doing anything with the file name it returns,
169      someone else may have beaten you to the punch.  :func:`mktemp` usage can
170      be replaced easily with :func:`NamedTemporaryFile`, passing it the
171      ``delete=False`` parameter::
172
173         >>> f = NamedTemporaryFile(delete=False)
174         >>> f
175         <open file '<fdopen>', mode 'w+b' at 0x384698>
176         >>> f.name
177         '/var/folders/5q/5qTPn6xq2RaWqk+1Ytw3-U+++TI/-Tmp-/tmpG7V1Y0'
178         >>> f.write("Hello World!\n")
179         >>> f.close()
180         >>> os.unlink(f.name)
181         >>> os.path.exists(f.name)
182         False
183
184The module uses two global variables that tell it how to construct a
185temporary name.  They are initialized at the first call to any of the
186functions above.  The caller may change them, but this is discouraged; use
187the appropriate function arguments, instead.
188
189
190.. data:: tempdir
191
192   When set to a value other than ``None``, this variable defines the
193   default value for the *dir* argument to all the functions defined in this
194   module.
195
196   If ``tempdir`` is unset or ``None`` at any call to any of the above
197   functions, Python searches a standard list of directories and sets
198   *tempdir* to the first one which the calling user can create files in.
199   The list is:
200
201   #. The directory named by the :envvar:`TMPDIR` environment variable.
202
203   #. The directory named by the :envvar:`TEMP` environment variable.
204
205   #. The directory named by the :envvar:`TMP` environment variable.
206
207   #. A platform-specific location:
208
209      * On RiscOS, the directory named by the :envvar:`Wimp$ScrapDir` environment
210        variable.
211
212      * On Windows, the directories :file:`C:\\TEMP`, :file:`C:\\TMP`,
213        :file:`\\TEMP`, and :file:`\\TMP`, in that order.
214
215      * On all other platforms, the directories :file:`/tmp`, :file:`/var/tmp`, and
216        :file:`/usr/tmp`, in that order.
217
218   #. As a last resort, the current working directory.
219
220
221.. function:: gettempdir()
222
223   Return the directory currently selected to create temporary files in. If
224   :data:`tempdir` is not ``None``, this simply returns its contents; otherwise,
225   the search described above is performed, and the result returned.
226
227   .. versionadded:: 2.3
228
229
230.. data:: template
231
232   .. deprecated:: 2.0
233      Use :func:`gettempprefix` instead.
234
235   When set to a value other than ``None``, this variable defines the prefix of the
236   final component of the filenames returned by :func:`mktemp`.  A string of six
237   random letters and digits is appended to the prefix to make the filename unique.
238   The default prefix is :file:`tmp`.
239
240   Older versions of this module used to require that ``template`` be set to
241   ``None`` after a call to :func:`os.fork`; this has not been necessary since
242   version 1.5.2.
243
244
245.. function:: gettempprefix()
246
247   Return the filename prefix used to create temporary files.  This does not
248   contain the directory component.  Using this function is preferred over reading
249   the *template* variable directly.
250
251   .. versionadded:: 1.5.2
252