334 lines
14 KiB
ReStructuredText
334 lines
14 KiB
ReStructuredText
:mod:`tempfile` --- Generate temporary files and directories
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============================================================
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.. module:: tempfile
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:synopsis: Generate temporary files and directories.
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.. sectionauthor:: Zack Weinberg <zack@codesourcery.com>
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**Source code:** :source:`Lib/tempfile.py`
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.. index::
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pair: temporary; file name
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pair: temporary; file
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--------------
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This module creates temporary files and directories. It works on all
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supported platforms. :class:`TemporaryFile`, :class:`NamedTemporaryFile`,
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:class:`TemporaryDirectory`, and :class:`SpooledTemporaryFile` are high-level
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interfaces which provide automatic cleanup and can be used as
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context managers. :func:`mkstemp` and
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:func:`mkdtemp` are lower-level functions which require manual cleanup.
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All the user-callable functions and constructors take additional arguments which
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allow direct control over the location and name of temporary files and
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directories. Files names used by this module include a string of
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random characters which allows those files to be securely created in
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shared temporary directories.
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To maintain backward compatibility, the argument order is somewhat odd; it
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is recommended to use keyword arguments for clarity.
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The module defines the following user-callable items:
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.. function:: TemporaryFile(mode='w+b', buffering=None, encoding=None, newline=None, suffix=None, prefix=None, dir=None)
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Return a :term:`file-like object` that can be used as a temporary storage area.
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The file is created securely, using the same rules as :func:`mkstemp`. It will be destroyed as soon
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as it is closed (including an implicit close when the object is garbage
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collected). Under Unix, the directory entry for the file is either not created at all or is removed
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immediately after the file is created. Other platforms do not support
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this; your code should not rely on a temporary file created using this
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function having or not having a visible name in the file system.
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The resulting object can be used as a context manager (see
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:ref:`tempfile-examples`). On completion of the context or
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destruction of the file object the temporary file will be removed
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from the filesystem.
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The *mode* parameter defaults to ``'w+b'`` so that the file created can
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be read and written without being closed. Binary mode is used so that it
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behaves consistently on all platforms without regard for the data that is
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stored. *buffering*, *encoding* and *newline* are interpreted as for
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:func:`open`.
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The *dir*, *prefix* and *suffix* parameters have the same meaning and
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defaults as with :func:`mkstemp`.
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The returned object is a true file object on POSIX platforms. On other
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platforms, it is a file-like object whose :attr:`!file` attribute is the
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underlying true file object.
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The :py:data:`os.O_TMPFILE` flag is used if it is available and works
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(Linux-specific, requires Linux kernel 3.11 or later).
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.. versionchanged:: 3.5
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The :py:data:`os.O_TMPFILE` flag is now used if available.
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.. function:: NamedTemporaryFile(mode='w+b', buffering=None, encoding=None, newline=None, suffix=None, prefix=None, dir=None, delete=True)
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This function operates exactly as :func:`TemporaryFile` does, except that
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the file is guaranteed to have a visible name in the file system (on
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Unix, the directory entry is not unlinked). That name can be retrieved
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from the :attr:`name` attribute of the returned
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file-like object. Whether the name can be
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used to open the file a second time, while the named temporary file is
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still open, varies across platforms (it can be so used on Unix; it cannot
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on Windows NT or later). If *delete* is true (the default), the file is
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deleted as soon as it is closed.
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The returned object is always a file-like object whose :attr:`!file`
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attribute is the underlying true file object. This file-like object can
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be used in a :keyword:`with` statement, just like a normal file.
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.. function:: SpooledTemporaryFile(max_size=0, mode='w+b', buffering=None, encoding=None, newline=None, suffix=None, prefix=None, dir=None)
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This function operates exactly as :func:`TemporaryFile` does, except that
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data is spooled in memory until the file size exceeds *max_size*, or
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until the file's :func:`fileno` method is called, at which point the
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contents are written to disk and operation proceeds as with
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:func:`TemporaryFile`.
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The resulting file has one additional method, :func:`rollover`, which
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causes the file to roll over to an on-disk file regardless of its size.
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The returned object is a file-like object whose :attr:`_file` attribute
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is either an :class:`io.BytesIO` or :class:`io.StringIO` object (depending on
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whether binary or text *mode* was specified) or a true file
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object, depending on whether :func:`rollover` has been called. This
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file-like object can be used in a :keyword:`with` statement, just like
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a normal file.
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.. versionchanged:: 3.3
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the truncate method now accepts a ``size`` argument.
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.. function:: TemporaryDirectory(suffix=None, prefix=None, dir=None)
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This function securely creates a temporary directory using the same rules as :func:`mkdtemp`.
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The resulting object can be used as a context manager (see
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:ref:`tempfile-examples`). On completion of the context or destruction
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of the temporary directory object the newly created temporary directory
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and all its contents are removed from the filesystem.
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The directory name can be retrieved from the :attr:`name` attribute of the
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returned object. When the returned object is used as a context manager, the
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:attr:`name` will be assigned to the target of the :keyword:`!as` clause in
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the :keyword:`with` statement, if there is one.
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The directory can be explicitly cleaned up by calling the
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:func:`cleanup` method.
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.. versionadded:: 3.2
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.. function:: mkstemp(suffix=None, prefix=None, dir=None, text=False)
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Creates a temporary file in the most secure manner possible. There are
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no race conditions in the file's creation, assuming that the platform
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properly implements the :const:`os.O_EXCL` flag for :func:`os.open`. The
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file is readable and writable only by the creating user ID. If the
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platform uses permission bits to indicate whether a file is executable,
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the file is executable by no one. The file descriptor is not inherited
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by child processes.
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Unlike :func:`TemporaryFile`, the user of :func:`mkstemp` is responsible
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for deleting the temporary file when done with it.
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If *suffix* is not ``None``, the file name will end with that suffix,
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otherwise there will be no suffix. :func:`mkstemp` does not put a dot
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between the file name and the suffix; if you need one, put it at the
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beginning of *suffix*.
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If *prefix* is not ``None``, the file name will begin with that prefix;
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otherwise, a default prefix is used. The default is the return value of
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:func:`gettempprefix` or :func:`gettempprefixb`, as appropriate.
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If *dir* is not ``None``, the file will be created in that directory;
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otherwise, a default directory is used. The default directory is chosen
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from a platform-dependent list, but the user of the application can
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control the directory location by setting the *TMPDIR*, *TEMP* or *TMP*
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environment variables. There is thus no guarantee that the generated
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filename will have any nice properties, such as not requiring quoting
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when passed to external commands via ``os.popen()``.
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If any of *suffix*, *prefix*, and *dir* are not
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``None``, they must be the same type.
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If they are bytes, the returned name will be bytes instead of str.
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If you want to force a bytes return value with otherwise default behavior,
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pass ``suffix=b''``.
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If *text* is specified, it indicates whether to open the file in binary
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mode (the default) or text mode. On some platforms, this makes no
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difference.
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:func:`mkstemp` returns a tuple containing an OS-level handle to an open
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file (as would be returned by :func:`os.open`) and the absolute pathname
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of that file, in that order.
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.. versionchanged:: 3.5
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*suffix*, *prefix*, and *dir* may now be supplied in bytes in order to
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obtain a bytes return value. Prior to this, only str was allowed.
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*suffix* and *prefix* now accept and default to ``None`` to cause
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an appropriate default value to be used.
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.. function:: mkdtemp(suffix=None, prefix=None, dir=None)
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Creates a temporary directory in the most secure manner possible. There
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are no race conditions in the directory's creation. The directory is
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readable, writable, and searchable only by the creating user ID.
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The user of :func:`mkdtemp` is responsible for deleting the temporary
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directory and its contents when done with it.
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The *prefix*, *suffix*, and *dir* arguments are the same as for
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:func:`mkstemp`.
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:func:`mkdtemp` returns the absolute pathname of the new directory.
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.. versionchanged:: 3.5
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*suffix*, *prefix*, and *dir* may now be supplied in bytes in order to
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obtain a bytes return value. Prior to this, only str was allowed.
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*suffix* and *prefix* now accept and default to ``None`` to cause
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an appropriate default value to be used.
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.. function:: gettempdir()
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Return the name of the directory used for temporary files. This
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defines the default value for the *dir* argument to all functions
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in this module.
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Python searches a standard list of directories to find one which
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the calling user can create files in. The list is:
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#. The directory named by the :envvar:`TMPDIR` environment variable.
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#. The directory named by the :envvar:`TEMP` environment variable.
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#. The directory named by the :envvar:`TMP` environment variable.
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#. A platform-specific location:
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* On Windows, the directories :file:`C:\\TEMP`, :file:`C:\\TMP`,
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:file:`\\TEMP`, and :file:`\\TMP`, in that order.
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* On all other platforms, the directories :file:`/tmp`, :file:`/var/tmp`, and
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:file:`/usr/tmp`, in that order.
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#. As a last resort, the current working directory.
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The result of this search is cached, see the description of
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:data:`tempdir` below.
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.. function:: gettempdirb()
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Same as :func:`gettempdir` but the return value is in bytes.
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.. versionadded:: 3.5
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.. function:: gettempprefix()
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Return the filename prefix used to create temporary files. This does not
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contain the directory component.
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.. function:: gettempprefixb()
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Same as :func:`gettempprefix` but the return value is in bytes.
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.. versionadded:: 3.5
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The module uses a global variable to store the name of the directory
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used for temporary files returned by :func:`gettempdir`. It can be
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set directly to override the selection process, but this is discouraged.
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All functions in this module take a *dir* argument which can be used
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to specify the directory and this is the recommended approach.
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.. data:: tempdir
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When set to a value other than ``None``, this variable defines the
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default value for the *dir* argument to the functions defined in this
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module.
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If ``tempdir`` is ``None`` (the default) at any call to any of the above
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functions except :func:`gettempprefix` it is initialized following the
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algorithm described in :func:`gettempdir`.
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.. _tempfile-examples:
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Examples
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--------
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Here are some examples of typical usage of the :mod:`tempfile` module::
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>>> import tempfile
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# create a temporary file and write some data to it
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>>> fp = tempfile.TemporaryFile()
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>>> fp.write(b'Hello world!')
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# read data from file
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>>> fp.seek(0)
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>>> fp.read()
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b'Hello world!'
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# close the file, it will be removed
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>>> fp.close()
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# create a temporary file using a context manager
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>>> with tempfile.TemporaryFile() as fp:
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... fp.write(b'Hello world!')
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... fp.seek(0)
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... fp.read()
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b'Hello world!'
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>>>
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# file is now closed and removed
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# create a temporary directory using the context manager
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>>> with tempfile.TemporaryDirectory() as tmpdirname:
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... print('created temporary directory', tmpdirname)
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>>>
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# directory and contents have been removed
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Deprecated functions and variables
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----------------------------------
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A historical way to create temporary files was to first generate a
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file name with the :func:`mktemp` function and then create a file
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using this name. Unfortunately this is not secure, because a different
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process may create a file with this name in the time between the call
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to :func:`mktemp` and the subsequent attempt to create the file by the
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first process. The solution is to combine the two steps and create the
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file immediately. This approach is used by :func:`mkstemp` and the
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other functions described above.
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.. function:: mktemp(suffix='', prefix='tmp', dir=None)
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.. deprecated:: 2.3
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Use :func:`mkstemp` instead.
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Return an absolute pathname of a file that did not exist at the time the
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call is made. The *prefix*, *suffix*, and *dir* arguments are similar
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to those of :func:`mkstemp`, except that bytes file names, ``suffix=None``
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and ``prefix=None`` are not supported.
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.. warning::
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Use of this function may introduce a security hole in your program. By
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the time you get around to doing anything with the file name it returns,
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someone else may have beaten you to the punch. :func:`mktemp` usage can
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be replaced easily with :func:`NamedTemporaryFile`, passing it the
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``delete=False`` parameter::
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>>> f = NamedTemporaryFile(delete=False)
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>>> f.name
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'/tmp/tmptjujjt'
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>>> f.write(b"Hello World!\n")
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13
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>>> f.close()
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>>> os.unlink(f.name)
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>>> os.path.exists(f.name)
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False
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