程式扎記: [Python Std Library] File and Directory Access : tempfile — Generate temporary files and directories

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2012年5月10日 星期四

[Python Std Library] File and Directory Access : tempfile — Generate temporary files and directories


參考自 這裡
Preface :
This module generates temporary files and directories. It works on all supported platforms.

In version 2.3 of Python, this module was overhauled for enhanced security. It now provides three new functions, NamedTemporaryFile()mkstemp(), and mkdtemp(), which should eliminate all remaining need to use the insecure 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 and template variables.

Supported APIs :
The module defines the following user-callable functions :
tempfile.TemporaryFile([mode='w+b'[, bufsize=-1[, suffix=''[, prefix='tmp'[, dir=None]]]]])
Return a file-like object that can be used as a temporary storage area. The file is created using 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. bufsize defaults to -1, meaning that the operating system default is used.

The dirprefix and suffix parameters are passed to mkstemp().

tempfile.NamedTemporaryFile([mode='w+b'[, bufsize=-1[, suffix=''[, prefix='tmp'[, dir=None[, delete=True]]]]]])
New in version 2.3.
New in version 2.6: The delete parameter.

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 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.

tempfile.SpooledTemporaryFile([max_size=0[, mode='w+b'[, bufsize=-1[, suffix=''[, prefix='tmp'[, dir=None]]]]]])
New in version 2.6.
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.

tempfile.mkstemp([suffix=''[, prefix='tmp'[, dir=None[, text=False]]]])
New in version 2.3.
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 theos.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 this api 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. This api does not put a dot between the file name and the suffix; if you need one, put it at the beginning of suffix.

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 TMPDIRTEMP or TMP environment variables.

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

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.

This api 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.
>>> tf = tempfile.mkstemp(suffix='.tmp', prefix='john')
>>> tf
(3, 'c:\\users\\john\\appdata\\local\\temp\\johncpv5ll.tmp') # 產生暫存檔 c:\\users\\john\\appdata\\local\\temp\\johncpv5ll.tmp
>>> os.write(tf[0], 'test string'.encode('utf-8'))
11 # 總共寫入 11 bytes
>>> os.close(tf[0])

tempfile.mkdtemp([suffix=''[, prefix='tmp'[, dir=None]]])
New in version 2.3.
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 this API is responsible for deleting the temporary directory and its contents when done with it.

The prefixsuffix, and dir arguments are the same as for mkstemp().

This API returns the absolute pathname of the new directory.

Global Variables :
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.
tempfile.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 :

tempfile.gettempdir()
New in version 2.3.
Return the directory currently selected to create temporary files in. If tempdir is not None, this simply returns its contents; otherwise, the search described above is performed, and the result returned.

tempfile.gettempprefix()
New in version 1.5.2.
Return the filename prefix used to create temporary files. This does not contain the directory component.

Supplement :
[Python Std Library] Built-in Types : File Objects
File objects are implemented using C’s stdio package and can be created with the built-in open() function...

stackoverflow > TypeError: 'str' does not support the buffer interface
If you use Python3x then string is not the same type as for Python 2.x, you must cast it to bytes (encode it)....

This message was edited 28 times. Last update was at 11/05/2012 09:49:01

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