Python 2.5b1 (r25b1:47027, Jun 20 2006, 09:31:33)

Assuming documentation is correct: (from seek() help
"Note that if the file is opened for appending (mode
'a' or 'a+'), any seek() operations will be undone at
the next write"

Doing the following is __not__ undoing the seek
operation after calling this a few times (Simplified
code snippet):

from __future__ import with_statement
with open(path,'a+') as f:
    f.seek(0,2) # go to end
    pos = f.tell() 
    f.seek(0,0)
    line = f.readline().strip()
    f.seek(0,2) # go to end, not effective if opened
with mode a/a+ (currently bug?)
    f.write("something")

Calling the above code repeatedly didnt increase the
file size beyond 166 bytes (in my code)