[Tutor] re-reading file-like objects

[Kent Johnson]

Tiago Saboga wrote:
> Hi!
> 
> I have a problem with file-like objects for months now, and I hoped I could 
> cope with it, but I keep using what seems to me like a newbie workaround...
> 
> The question is: how can I read a file (more precisely, a file-like object) 
> more than one single time? 
> 
> In the following example, I want to generate a file in memory and save it with 
> ten different names. But I can't do it with shutil.copyfileobj, AFAICS 
> because it reads the file with read() method, which can only be used once. If 
> it's a real file, on disk, I agree it would not be a clever strategy, reading 
> it once for each copy, and I would be happy keeping its content in a 
> variable. But if the file is in memory, why can't I simply read it again (or 
> better, how can I...)?
> 
> ====================successful==================
> import subprocess
> 
> FILESIZE = 200000
> NUMBER = 10
> DIR = '/tmp/pytest'
> FILENAME = 'treco.x'
> 
> basefilecontents = 
> subprocess.Popen(['dd', 'if=/dev/zero', 'count=1', 'bs=%s' % FILESIZE], 
> stdout=subprocess.PIPE, bufsize=FILESIZE).stdout.read()
> 
> for i in range(NUMBER):
> 	print "File number %s" % i
> 	newfile = open('%s/%s%s' % (DIR, FILENAME, i), 'w')
> 	newfile.write(basefilecontents)
> 	newfile.close()

Your input file isn't 'in memory', it is the output of a subprocess. To
read the input again, the subprocess would have to create the output again.

This solution seems fine to me - you read the input file *contents* into 
memory, then write it to multiple files. Why don't you like this approach?

Kent