django.core.files.base.File enhancement / fix

[nickname123]

Hi,

I think that django.core.files.base.File should be expanded to handle a wider range of file objects. In my specific case, StringIO/cStringIO and tempfile.SpooledTemporaryFile objects.

Here is a simple demonstration of where the File class breaks:

from tempfile import SpooledTemporaryFile
from django.core.files import File
f = SpooledTemporaryFile(
		max_size    = 1024,# 1kb
		mode        = 'w+b',# must be open in binary mode
		bufsize     = -1,
		suffix      = '',
		prefix      = 'tmp',
		dir         = None
)
f.write("hello")
print len(File(f))

Here is the result (on Windows using Python2.6):

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\...\django\core\files\base.py", line 33, in __len__
    return self.size
  File "C:\...\django\core\files\base.py", line 39, in _get_size
    elif os.path.exists(self.file.name):
  File "C:\...\lib\tempfile.py", line 559, in name
    return self._file.name
AttributeError: 'cStringIO.StringO' object has no attribute 'name'

It should be noted that not only does the current implementation fail, but it breaks in the wrong code block because it doesn't verify that the name attribute is available.

I propose that the file objects seek and tell method be used as an additional fallback before throwing the attribute error as follows:

def _get_size(self):
	if not hasattr(self, '_size'):
		if hasattr(self.file, 'size'):
			self._size = self.file.size
		elif hasattr(self.file, 'name') and os.path.exists(self.file.name):
			self._size = os.path.getsize(self.file.name)
		elif hasattr(self.file, 'tell') and hasattr(self.file, 'seek'):
			pos = self.file.tell()
			self.file.seek(0,os.SEEK_END)
			self._size = self.file.tell()
			self.file.seek(pos)
		else:
			raise AttributeError("Unable to determine the file's size.")
	return self._size

My proposed patch fixes the problems mentioned above.

[nickname123]

patch

[Jacob]

Milestone 1.3 deleted

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Change Easy pickings from NULL to False.

[Claude Paroz]

Patch with tests

[Claude Paroz]

I've reviewed the File documentation (​https://docs.djangoproject.com/en/dev/ref/files/file/), but didn't find any complement to add related to this fix.

Changed Type to bug because of the error raised by _get_size when the underlying file object has no name (see also #16946 which is a duplicate).

[Michael Palumbo <michael.palumbo87@…>]

That would be nice to make the File object more file-like object so that we could use the File Storage API with any file-like objects (e.g. with what urllib2.urlopen returns)
Because as for now, this does not work for the main reason said previously (elif os.path.exists(self.file.name):

import urllib2
from django.core.files.base import File
from django.core.files.storage import FileSystemStorage
url = 'http://www.google.fr'
fs = FileSystemStorage(location='./here/')
f = File(urllib2.urlopen(urllib2.Request(url)))
fs.save("downloaded_file.html", f)

Is it planned to be changed ? Maybe for django 1.4 ? How can we help ?

Thanks.

[Michael Palumbo <michael.palumbo87@…>]

I added a new patch because the chunks method of the File object did not work with urllib2.urlopen().
Indeed, this method was using the size which is unknown in this case.
I completed claudep's patch.

[anonymous]

I think this is good to go.

[Claude Paroz]

In [17871]:

Fixed #15644 -- Improved Django File wrapper to support more file-like objects. Thanks nickname123 and Michael Palumbo for working on the patch.

[Collin Anderson]

(this was actually a dup of #8501)