I have a file, which I can decompress under linux using the following command:

unxz < file.xz > file.txt

How can I do the same using python? If I use python3 and the tarfile module and do the following:

import sys
import tarfile
try:
    with tarfile.open('temp.xz', 'r:xz') as t:
        t.extract()
except Exception as e:
    print("Error:", e.strerror)

I get the exception: ReadError('invalid header',). So apparently it expects some file- or directory information which is not present in the xz file.

So how can I decompress a file without header information?

The tarfile module is only for... err... tar files. What you have here is not one.

XZ support is available in Python 3.3's LZMA module. In Python 2.x, you need backports.lzma.

try:
    import lzma
except ImportError:
    from backports import lzma

print lzma.open('file.xz').read()