Managing files¶

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:

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
u'cars/chevy.jpg'
>>> car.photo.path
u'/media/cars/chevy.jpg'
>>> car.photo.url
u'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.

The File object¶

Internally, Django uses a django.core.files.File instance any time it needs to represent a file. This object is a thin wrapper around Python’s built-in file object with some Django-specific additions.

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('/tmp/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('/tmp/hello.world', 'w') as f:
>>>     myfile = File(f)
>>>     for line in myfile:
>>>         print line
>>> myfile.closed
True
>>> 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.

>>> from django.core.files.storage import default_storage
>>> from django.core.files.base import ContentFile

>>> path = default_storage.save('/path/to/file', ContentFile('new content'))
>>> path
u'/path/to/file'

>>> default_storage.size(path)
11
>>> default_storage.open(path).read()
'new content'

>>> default_storage.delete(path)
>>> default_storage.exists(path)
False

from django.db import models
from django.core.files.storage import FileSystemStorage

fs = FileSystemStorage(location='/media/photos')

class Car(models.Model):
    ...
    photo = models.ImageField(storage=fs)