Per Erik Strandberg /cv /kurser /blog

I always forget basic usage of the tempfile module in python, so I made a summary of what I typically use. As it turns out some basic knowledge of filehandles and the os module may also help.

NamedTemporaryFile

From the Python documentation: 

NamedTemporaryFile( [mode="w+b"[, bufsize=-1[, 
     suffix=""[, prefix="tmp"[, dir=None[, 
     delete=True]]]]]])

[...] the file is guaranteed to have a visible name in the file system [...] can be retrieved from the name attribute of the file object. [...] If delete is true [...] deleted as soon as it is closed.

A short example of how you typically use a NamedTemporaryFile - with no special parameters. Note that the file is deleted upon close.

>>> from tempfile import NamedTemporaryFile
>>> from os.path import exists
>>> ntf = NamedTemporaryFile()
>>> ntf.name
'/tmp/tmpGFJp4a'
>>> exists( ntf.name )
True
>>> ntf.write( "it's not dead it's just resting" )
>>> ntf.seek( 9 )
>>> ntf.read( 4 )
'dead'
>>> ntf.close()
>>> exists( ntf.name )
False

A slightly longer example where the user has to manually delete (aka "unlink") the file.

>>> from tempfile import NamedTemporaryFile
>>> from os.path import exists
>>> from os import unlink
>>> ntf = NamedTemporaryFile( suffix=".tmp", prefix="tmp_", delete=False )
>>> ntf.write( 'foo' )
>>> ntf.seek( 1 )
>>> ntf.read()
'oo'
>>> name = ntf.name
>>> name
'/tmp/tmp_wFNKmo.tmp'
>>> ntf.close()
>>> exists( name )
True
>>> unlink( name )
>>> exists( name )
False

mkstemp

Again, from the Python documentation:

mkstemp( [suffix=""[, prefix="tmp"[, dir=None[, text=False]]]])

Creates a temporary file in the most secure manner possible. [...] Unlike TemporaryFile(), the user of mkstemp() is responsible for deleting the temporary file when done with it. [...] mkstemp() 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 [...]

>>> from tempfile import mkstemp
>>> from os.path import exists
>>> from os import unlink, close, write
>>> ( handle, name ) = mkstemp( suffix = ".data", prefix = "sensor_" )
>>> type( handle )
<type 'int'>
>>> type( name )
<type 'str'>
>>> name
'/tmp/sensor_Cmdtrk.data'
>>> write( handle, 'foobie bletch' )
13
>>> close( handle )
>>> exists( name )
True
>>> f = open( name, 'r')
>>> f.read()
'foobie bletch'
>>> f.close()
>>> exists( name )
True
>>> unlink( name )
>>> exists( name )
False

Just a random temporary filename

This could be a start if you just want a random temporary filename.

>>> from tempfile import gettempdir, gettempprefix
>>> from os.path import join
>>> join( gettempdir(), gettempprefix() )
'/tmp/tmp'

Or perhaps something longer like this:

>>> from tempfile import gettempdir, gettempprefix
>>> from os.path import join
>>> from string import ascii_lowercase, digits
>>> from random import choice
>>> 
>>> ( suffix1, suffix2 ) = ( "", "" )
>>>
>>> for _ in xrange( 8 ):
...     suffix1 += choice( ascii_lowercase )
...     suffix2 += choice( digits )
... 
>>> print join( gettempdir(), '-'.join( [ gettempprefix(), suffix1, suffix2 ] ) )
/tmp/tmp-bsanoyzp-53044506

But remember that there is no guarantee that this filename is unique, so I would use some checks to see that the filename is ok before I started using it.

Tillhör Kategori Programmering