Managing files. Django Software

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