tempfile – Create temporary filesystem resources.

Purpose:Create temporary filesystem resources.
Available In:Since 1.4 with major security revisions in 2.3

Many programs need to create files to write intermediate data. Creating files with unique names securely, so they cannot be guessed by someone wanting to break the application, is challenging. The tempfile module provides several functions for creating filesystem resources securely. TemporaryFile() opens and returns an un-named file, NamedTemporaryFile() opens and returns a named file, and mkdtemp() creates a temporary directory and returns its name.

TemporaryFile

If your application needs a temporary file to store data, but does not need to share that file with other programs, the best option for creating the file is the TemporaryFile() function. It creates a file, and on platforms where it is possible, unlinks it immediately. This makes it impossible for another program to find or open the file, since there is no reference to it in the filesystem table. The file created by TemporaryFile() is removed automatically when it is closed.

import os
import tempfile

print 'Building a file name yourself:'
filename = '/tmp/guess_my_name.%s.txt' % os.getpid()
temp = open(filename, 'w+b')
try:
    print 'temp:', temp
    print 'temp.name:', temp.name
finally:
    temp.close()
    # Clean up the temporary file yourself
    os.remove(filename)

print
print 'TemporaryFile:'
temp = tempfile.TemporaryFile()
try:
    print 'temp:', temp
    print 'temp.name:', temp.name
finally:
    # Automatically cleans up the file
    temp.close()

This example illustrates the difference in creating a temporary file using a common pattern for making up a name, versus using the TemporaryFile() function. Notice that the file returned by TemporaryFile() has no name.

$ python tempfile_TemporaryFile.py

Building a file name yourself:
temp: <open file '/tmp/guess_my_name.14891.txt', mode 'w+b' at 0x100458270>
temp.name: /tmp/guess_my_name.14891.txt

TemporaryFile:
temp: <open file '<fdopen>', mode 'w+b' at 0x100458780>
temp.name: <fdopen>

By default, the file handle is created with mode 'w+b' so it behaves consistently on all platforms and your program can write to it and read from it.

import os
import tempfile

temp = tempfile.TemporaryFile()
try:
    temp.write('Some data')
    temp.seek(0)
    
    print temp.read()
finally:
    temp.close()

After writing, you have to rewind the file handle using seek() in order to read the data back from it.

$ python tempfile_TemporaryFile_binary.py

Some data

If you want the file to work in text mode, set mode to 'w+t' when you create it:

import tempfile

f = tempfile.TemporaryFile(mode='w+t')
try:
    f.writelines(['first\n', 'second\n'])
    f.seek(0)

    for line in f:
        print line.rstrip()
finally:
    f.close()

The file handle treats the data as text:

$ python tempfile_TemporaryFile_text.py

first
second

NamedTemporaryFile

There are situations, however, where having a named temporary file is important. If your application spans multiple processes, or even hosts, naming the file is the simplest way to pass it between parts of the application. The NamedTemporaryFile() function creates a file with a name, accessed from the name attribute.

import os
import tempfile

temp = tempfile.NamedTemporaryFile()
try:
    print 'temp:', temp
    print 'temp.name:', temp.name
finally:
    # Automatically cleans up the file
    temp.close()
print 'Exists after close:', os.path.exists(temp.name)

Even though the file is named, it is still removed after the handle is closed.

$ python tempfile_NamedTemporaryFile.py

temp: <open file '<fdopen>', mode 'w+b' at 0x100458270>
temp.name: /var/folders/5q/8gk0wq888xlggz008k8dr7180000hg/T/tmpIIkknb
Exists after close: False

mkdtemp

If you need several temporary files, it may be more convenient to create a single temporary directory and then open all of the files in that directory. To create a temporary directory, use mkdtemp().

import os
import tempfile

directory_name = tempfile.mkdtemp()
print directory_name
# Clean up the directory yourself
os.removedirs(directory_name)

Since the directory is not “opened” per se, you have to remove it yourself when you are done with it.

$ python tempfile_mkdtemp.py

/var/folders/5q/8gk0wq888xlggz008k8dr7180000hg/T/tmpE4plSY

Predicting Names

For debugging purposes, it is useful to be able to include some indication of the origin of the temporary files. While obviously less secure than strictly anonymous temporary files, including a predictable portion in the name lets you find the file to examine it while your program is using it. All of the functions described so far take three arguments to allow you to control the filenames to some degree. Names are generated using the formula:

dir + prefix + random + suffix

where all of the values except random can be passed as arguments to TemporaryFile(), NamedTemporaryFile(), and mkdtemp(). For example:

import tempfile

temp = tempfile.NamedTemporaryFile(suffix='_suffix', 
                                   prefix='prefix_', 
                                   dir='/tmp',
                                   )
try:
    print 'temp:', temp
    print 'temp.name:', temp.name
finally:
    temp.close()

The prefix and suffix arguments are combined with a random string of characters to build the file name, and the dir argument is taken as-is and used as the location of the new file.

$ python tempfile_NamedTemporaryFile_args.py

temp: <open file '<fdopen>', mode 'w+b' at 0x100458270>
temp.name: /tmp/prefix_SMkGcX_suffix

Temporary File Location

If you don’t specify an explicit destination using the dir argument, the actual path used for the temporary files will vary based on your platform and settings. The tempfile module includes two functions for querying the settings being used at runtime:

import tempfile

print 'gettempdir():', tempfile.gettempdir()
print 'gettempprefix():', tempfile.gettempprefix()

gettempdir() returns the default directory that will hold all of the temporary files and gettempprefix() returns the string prefix for new file and directory names.

$ python tempfile_settings.py

gettempdir(): /var/folders/5q/8gk0wq888xlggz008k8dr7180000hg/T
gettempprefix(): tmp

The value returned by gettempdir() is set based on a straightforward algorithm of looking through a list of locations for the first place the current process can create a file. From the library documentation:

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:

  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 RiscOS, the directory named by the Wimp$ScrapDir environment variable.
    • 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.

If your program needs to use a global location for all temporary files that you need to set explicitly but do not want to set through one of these environment variables, you can set tempfile.tempdir directly.

import tempfile

tempfile.tempdir = '/I/changed/this/path'
print 'gettempdir():', tempfile.gettempdir()
$ python tempfile_tempdir.py

gettempdir(): /I/changed/this/path

See also

tempfile
Standard library documentation for this module.
File Access
More modules for working with files.
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