[Tutor] using tarfile on strings or filelike objects

[Barton David]

Thanks Kent,

But.. I've actually found that that doesn't work (raises a ReadError),
and neither does..
>>>tf=tarfile.open(mode="r|*",fileobj=filelike)
..which raises "AttributeError: _Stream instance has no attribute
'dbuf'"

However if I explicitly state the compression type.. e.g.
>>>tf=tarfile.open(mode="r|bz2",fileobj=filelike)
..then I can indeed go on to..
>>>print tf.getnames()
>>>assert archive_member_name in tf.getnames()
..and it works ok. Having to explicitly state the compression type isn't
exactly ideal, but I guess it'll do me for now.

Unfortunately, I'm still having trouble actually reading the contents of
'archive_member'.
i.e. ..
>>>tf_filelike=tf.extractfile(archive_member_name)
>>>print tf_filelike.read()
..raises..
File "C:\Python24\lib\tarfile.py", line 551, in _readnormal
    self.fileobj.seek(self.offset + self.pos)
File "C:\Python24\lib\tarfile.py", line 420, in seek
    raise StreamError, "seeking backwards is not allowed"

And I get the same error if I instead try..
>>>tf_infoobject=tf.getmember(archive_member_name)
>>>tf_filelike=tf.extractfile(tf_infoobject)
>>>print tf_filelike.read()

In fact I'm getting this even if I open the archive by passing the path
name (rather than using fileobj) so I guess this isn't the problem I
initially thought it was. I just don't get it.

Regards,
Dave

-----Original Message-----
From: Kent Johnson [mailto:kent37 at tds.net] 
Sent: 03 March 2007 22:26
To: Barton David
Cc: tutor at python.org
Subject: Re: [Tutor] using tarfile on strings or filelike objects

Barton David wrote:
> I like that I can access the contents of a zip archive that's stored 
> in memory (rather than on disk) by packing the archive contents into a

> StringIO or cStringIO object and feeding that to ZipFile...
>  
> i.e.
>  
> filelike=cStringIO.StringIO(archive_as_string)
> zf=zipfile.ZipFile(filelike)
> content=zf.read(archive_member_name)
> zf.close()
> filelike.close()
>  
> but I can't get the same thing to work with TarFile. Is there any way 
> to do this? (Other than first saving the archive data to disk and then

> passing the path to TarFile.open?) The tarfile module documentation 
> talks about an optional fileobj flag but this doesn't seem to work.

Just from reading the docs I would try
filelike = cStringIO...
tf = tarfile.open(mode='r|', fileobj=filelike)

This is based on the example in the docs of reading from stdin.

Kent


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