[Python-talk] {Python-talk] Running off the end of a file during read?

[Christopher Schmidt]

On Sun, Jun 14, 2009 at 12:24:05PM -0400, Bruce Labitt wrote:
> Folks, I have been coding a binary datalog file reader for a colleague  
> of mine in the UK.  He bought a really cool RS232 datalogger that he  
> managed to hook up to an ECU (engine control unit).   I do a  read(56)  
> because  I am looking for a particular sequence.  My method works ok for  
> a file that contains multiple sessions, but fails on the last session (I  
> suspect) or on a file with ony one session.
>
> Basically I read 56 bytes then look for a sequence in it.  If I don't  
> find it I reset the file pointer so that it is incremented by 1 from the  
> start of the last 56 byte read.  The program keeps going until it finds  
> the right sequence. 
>
> Obviously, if either the sequence is not there, or one hits end of file  
> things would go haywire (program hang in my case).
>
> Does f.read(n) error if the function hits eof?  If not how can I  
> determine when I hit eof?

>>> f = open("123.txt")
>>> s = f.read(2); len(s)
2
>>> s = f.read(2); len(s)
2
>>> s = f.read(2); len(s)
0

Check your len(), compare it to your read() length, see if the numbers differ?
or is there something I'm missing here? 

Regards,
-- 
Christopher Schmidt
Web Developer