File read-write mode: problem appending after reading

[Frederic Rentsch]

Hi all,

   Working with read and write operations on a file I stumbled on a 
complication when writes fail following a read to the end.

 >>> f = file ('T:/z', 'r+b')
 >>> f.write ('abcdefg')
 >>> f.tell ()
30L
 >>> f.seek (0)
 >>> f.read ()
'abcdefg'
 >>> f.flush ()  # Calling or not makes no difference
 >>> f.write ('abcdefg')

Traceback (most recent call last):
  File "<pyshell#62>", line 1, in -toplevel-
    f.write ('abcdefg')
IOError: (0, 'Error')

Flushing doesn't help. I found two work arounds:

 >>> f.read ()
'abcdefg'
 >>> f.read ()   # Workaround 1: A second read (returning an empty string)
''
 >>> f.write ('abcdefg')
(No error)

 >>> f.read ()
'abcdefg'
 >>> f.seek (f.tell ())   # Workaround 2: Setting the cursor (to where 
it is!)
 >>> f.write ('abcdefg')
(No error)

I found no problem with writing into the file. So it looks like it has 
to do with the cursor which a read puts past the end, unless it is past 
the end, in which case it goes back to the end. Is there a less kludgy 
alternative to "fseek (ftell ())"?

Frederic