Django Documentation, Release 2.0.dev20170914110741
Managing files
This document describes Django’s file access APIs for files such as those uploaded by a user. The lower level APIs are general enough that you could use them for other purposes. If you want to handle “static files” (JS, CSS, etc.), see
Managing static files (e.g. images, JavaScript, CSS) .
By default, Django stores files locally, using the
MEDIA_ROOT
and
MEDIA_URL
settings. The examples below assume that you’re using these defaults.
However, Django provides ways to write custom
file storage systems
that allow you to completely customize where and how Django stores files. The second half of this document describes how these storage systems work.
Using files in models
When you use a
FileField
or
ImageField
, Django provides a set of APIs you can use to deal with that file.
Consider the following model, using an
ImageField
to store a photo:
from
django.db
import
models
class Car
(models.Model): name = models.CharField(max_length= 255 ) price = models.DecimalField(max_digits= 5 , decimal_places= 2 ) photo = models.ImageField(upload_to= 'cars' )
Any Car instance will have a photo attribute that you can use to get at the details of the attached photo:
>>> car = Car.objects.get(name= "57 Chevy" )
>>> car.photo
<ImageFieldFile: chevy.jpg>
>>> car.photo.name
'cars/chevy.jpg'
>>> car.photo.path
'/media/cars/chevy.jpg'
>>> car.photo.url
'http://media.example.com/cars/chevy.jpg'
This object – car.photo in the example – is a File object, which means it has all the methods and attributes described below.
Note: The file is saved as part of saving the model in the database, so the actual file name used on disk cannot be relied on until after the model has been saved.
For example, you can change the file name by setting the file’s
name
to a path relative to the file storage’s location
(
MEDIA_ROOT
if you are using the default
FileSystemStorage
):
>>>
import
os
>>>
from
django.conf
import
settings
>>> initial_path = car.photo.path
>>> car.photo.name = 'cars/chevy_ii.jpg'
>>> new_path = settings.MEDIA_ROOT + car.photo.name
>>> # Move the file on the filesystem
>>> os.rename(initial_path, new_path)
>>> car.save()
>>> car.photo.path
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Django Documentation, Release 2.0.dev20170914110741
'/media/cars/chevy_ii.jpg'
>>> car.photo.path == new_path
True
The File object
Internally, Django uses a
django.core.files.File
instance any time it needs to represent a file.
Most of the time you’ll simply use a File that Django’s given you (i.e. a file attached to a model as above, or perhaps an uploaded file).
If you need to construct a File yourself, the easiest way is to create one using a Python built-in file object:
>>>
from
django.core.files
import
File
# Create a Python file object using open()
>>> f = open ( '/path/to/hello.world' , 'w' )
>>> myfile = File(f)
Now you can use any of the documented attributes and methods of the
File
class.
Be aware that files created in this way are not automatically closed. The following approach may be used to close files automatically:
>>>
from
django.core.files
import
File
# Create a Python file object using open() and the with statement
>>>
with
open ( '/path/to/hello.world' , 'w' ) as f:
...
myfile = File(f)
...
...
myfile.write(
>>> myfile.closed
True
'Hello World' )
>>> f.closed
True
Closing files is especially important when accessing file fields in a loop over a large number of objects. If files are not manually closed after accessing them, the risk of running out of file descriptors may arise. This may lead to the following error:
IOError
: [Errno 24 ] Too many open files
File storage
Behind the scenes, Django delegates decisions about how and where to store files to a file storage system. This is the object that actually understands things like file systems, opening and reading files, etc.
Django’s default file storage is given by the
DEFAULT_FILE_STORAGE
setting; if you don’t explicitly provide a storage system, this is the one that will be used.
See below for details of the built-in default file storage system, and see
Writing a custom storage system
for information on writing your own file storage system.
318 Chapter 3. Using Django
