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