I always missed a getsize() method on file objects. The patch adds a
method getsize() to all io instances. The method returns a SizeInfo
object which can print a human readable name or the bare size in bytes.
The method is using os.fstat and falls back to the seek(0,2), tell()
pattern.

>>> f = open("/etc/passwd")
>>> f.getsize()
<SizeInfo 1.7 KiB>
>>> int(f.getsize())
1721
>>> str(f.getsize())
'1.7 KiB'
>>> (f.getsize().sizeinfo())
(1.681, 1)

I'm going to provide unit tests and documentation if you like the feature.