Size of an open file object

Is there a way to find the size of a file object that is currently open?

Specifically, I am working with the tarfile module to create tarfiles, but I don't want my tarfile to exceed a certain size. As far as I know, tarfile objects are file-like objects, so I imagine a generic solution would work.

$ ls -la chardet-1.0.1.tgz
-rwxr-xr-x 1 vinko vinko 179218 2008-10-20 17:49 chardet-1.0.1.tgz
$ python
Python 2.5.1 (r251:54863, Jul 31 2008, 22:53:39)
[GCC 4.1.2 (Ubuntu 4.1.2-0ubuntu4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> f = open('chardet-1.0.1.tgz','rb')
>>> f.seek(0,2)
>>> f.tell()
179218L

Adding ChrisJY's idea to the example

>>> import os
>>> os.fstat(f.fileno()).st_size
179218L
>>>        

Note: Based on the comments, f.seek(0, 2) is must before calling f.tell(), without which it would return a size of 0. The reason is that f.seek(0, 2) moves the file object's position to the end of the file.

Well, if the file object support the tell method, you can do:

current_size = f.tell()

That will tell you were it is currently writing. If you write in a sequential way this will be the size of the file.

Otherwise, you can use the file system capabilities, i.e. os.fstat as suggested by others.

If you have the file descriptor, you can use fstat to find out the size, if any. A more generic solution is to seek to the end of the file, and read its location there.

Another solution is using StringIO "if you are doing in-memory operations".

with open(file_path, 'rb') as x:
    body = StringIO()
    body.write(x.read())
    body.seek(0, 0)
 

Now body behaves like a file object with various attributes like body.read().

body.len gives the file size.

Nobody mentioned what to me seems the simplest way i.e using the len() function after a read:

>>> with open("C:\\path\\to\\a\\file.txt", 'rb') as f:
...     f_read = f.read()  
...     print(len(f_read))
... 
36