BufferedFile should have a 'closed' propery

[smunaut]

The Python file interface seems to publically define a xxx.closed property and some application use it.
Currently there is an internal _closed propery and just exposing it read-only works:

@property
def closed(self):
    return self._closed

[Bockit]

I ran into this problem today when running django's collectstatic function with the SFTP backend and some Pipeline'd files.

Traceback (most recent call last):
  File "./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/Users/work/Documents/business-development/smudtodo/venv/lib/python2.7/site-packages/django/core/management/__init__.py", line 443, in execute_from_command_line
    utility.execute()
  File "/Users/work/Documents/business-development/smudtodo/venv/lib/python2.7/site-packages/django/core/management/__init__.py", line 382, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Users/work/Documents/business-development/smudtodo/venv/lib/python2.7/site-packages/django/core/management/base.py", line 196, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/Users/work/Documents/business-development/smudtodo/venv/lib/python2.7/site-packages/django/core/management/base.py", line 232, in execute
    output = self.handle(*args, **options)
  File "/Users/work/Documents/business-development/smudtodo/venv/lib/python2.7/site-packages/django/core/management/base.py", line 371, in handle
    return self.handle_noargs(**options)
  File "/Users/work/Documents/business-development/smudtodo/venv/lib/python2.7/site-packages/django/contrib/staticfiles/management/commands/collectstatic.py", line 163, in handle_noargs
    collected = self.collect()
  File "/Users/work/Documents/business-development/smudtodo/venv/lib/python2.7/site-packages/django/contrib/staticfiles/management/commands/collectstatic.py", line 120, in collect
    for original_path, processed_path, processed in processor:
  File "/Users/work/Documents/business-development/smudtodo/venv/lib/python2.7/site-packages/django/contrib/staticfiles/storage.py", line 239, in post_process
    saved_name = self._save(hashed_name, original_file)
  File "/Users/work/Documents/business-development/smudtodo/venv/lib/python2.7/site-packages/storages/backends/sftpstorage.py", line 167, in _save
    content.open()
  File "/Users/work/Documents/business-development/smudtodo/venv/lib/python2.7/site-packages/django/core/files/base.py", line 111, in open
    if not self.closed:
  File "/Users/work/Documents/business-development/smudtodo/venv/lib/python2.7/site-packages/django/core/files/base.py", line 51, in _get_closed
    return not self.file or self.file.closed
AttributeError: 'SFTPFile' object has no attribute 'closed'

I eventually tracked it down to this issue (BufferedFile needing a closed property) and had the same solution as suggested.

[bitprophet]

Thanks to both of you, this fix works for now. (Reckon eventually we'll want to simply make the "private" var public.)