Unable to Concatenate a file - destination kept getting overwritten

[Dave Angel]

On 04/20/2012 09:03 PM, Foster Rilindo wrote:
> I can't seem to concatenate.
>
> I got binary files here:
>
> yvaine:disk rilindo$ ls -lah
> total 61440
> drwxr-xr-x   4 rilindo  staff   136B Apr 20 19:47 .
> drwxr-xr-x  10 rilindo  staff   340B Apr 20 19:45 ..
> -rw-r--r--   1 rilindo  staff    20M Apr 20 20:00 disk1
> -rw-r--r--   1 rilindo  staff    10M Apr 20 19:47 disk2
>
> Based on the following code, I should be able to cat disk2 over to disk 1, resulting in a 30 Meg file:
>
>>>> import shutil
>>>> import os
>>>> disk1="/Users/rilindo/tmp/disk/disk1"
>>>> disk2="/Users/rilindo/tmp/disk/disk2"
>>>> destination = open(disk1,'wb')
>>>> shutil.copyfileobj(open(disk2,'rb'),destination)
>>>> destination.close()
> However, the result is that the destination gets overwritten:
>
> yvaine:disk rilindo$ ls -lah
> total 40960
> drwxr-xr-x   4 rilindo  staff   136B Apr 20 19:47 .
> drwxr-xr-x  10 rilindo  staff   340B Apr 20 19:45 ..
> -rw-r--r--   1 rilindo  staff    10M Apr 20 20:02 disk1
> -rw-r--r--   1 rilindo  staff    10M Apr 20 19:47 disk2
>
> Is this right way to concatenate a file or is there a better way?
>
>  - Rilindo

I don't happen to be familiar with copyfileobj, but I can tell you that
the destination file is truncated even before the function is called.

destination = open(disk1,'wb')

will truncate the file before it returns the file object.  You probably want  'a+b' rather than 'wb'

I still don't know if copyfileobj will do what you want, but you should be closer now.



-- DaveA