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9c7927400c
The case of tempfile.tempdir variable being bytes is now handled consistently. The getters return the right type and no more error of mixing str and bytes unless explicitly caused by the user. Adds a regression test. Expands the documentation to clarify the behavior. Co-authored-by: Eric L <ewl+git@lavar.de> Co-authored-by: Gregory P. Smith <greg@krypto.org>
374 lines
15 KiB
ReStructuredText
374 lines
15 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=-1, encoding=None, newline=None, suffix=None, prefix=None, dir=None, *, errors=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*, *errors* 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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.. audit-event:: tempfile.mkstemp fullpath tempfile.TemporaryFile
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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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.. versionchanged:: 3.8
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Added *errors* parameter.
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.. function:: NamedTemporaryFile(mode='w+b', buffering=-1, encoding=None, newline=None, suffix=None, prefix=None, dir=None, delete=True, *, errors=None)
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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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.. audit-event:: tempfile.mkstemp fullpath tempfile.NamedTemporaryFile
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.. versionchanged:: 3.8
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Added *errors* parameter.
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.. function:: SpooledTemporaryFile(max_size=0, mode='w+b', buffering=-1, encoding=None, newline=None, suffix=None, prefix=None, dir=None, *, errors=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.TextIOWrapper` object
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(depending on 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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.. versionchanged:: 3.8
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Added *errors* parameter.
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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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.. audit-event:: tempfile.mkdtemp fullpath tempfile.TemporaryDirectory
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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 and true, the file is opened in text mode.
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Otherwise, (the default) the file is opened in binary mode.
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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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.. audit-event:: tempfile.mkstemp fullpath tempfile.mkstemp
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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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.. versionchanged:: 3.6
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The *dir* parameter now accepts a :term:`path-like object`.
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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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.. audit-event:: tempfile.mkdtemp fullpath tempfile.mkdtemp
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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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.. versionchanged:: 3.6
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The *dir* parameter now accepts a :term:`path-like object`.
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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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.. versionchanged:: 3.10
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Always returns a str. Previously it would return any :data:`tempdir`
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value regardless of type so long as it was not ``None``.
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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. This is the recommended approach that does
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not surprise other unsuspecting code by changing global API behavior.
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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, including its type, bytes or str. It cannot be a
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:term:`path-like object`.
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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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.. note::
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Beware that if you set ``tempdir`` to a bytes value, there is a
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nasty side effect: The global default return type of
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:func:`mkstemp` and :func:`mkdtemp` changes to bytes when no
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explicit ``prefix``, ``suffix``, or ``dir`` arguments of type
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str are supplied. Please do not write code expecting or
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depending on this. This awkward behavior is maintained for
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compatibility with the historcal implementation.
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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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