Unable to use xopen handle as output of subprocess (`io.UnsupportedOperation: fileno`)

My goal is to run a shell command and stream the output to a compressed file. I figured xopen would be a good way to achieve this, however I can't get it to work. Here is a minimal reproducible example: ```py from xopen import xopen from subprocess import run with xopen("file1.txt", "w") as f: f.write("something") with xopen("file2.txt.xz", "wb") as f: run(["cat", "file1.txt"], stdout=f) # also tried: # • Popen(["cat", "file1.txt"], stdout=f) # • call(["cat", "file1.txt"], stdout=f) # • output file extension of .gz, .zst ``` Error: ``` File "test.py", line 8, in <module> run(["cat", "file1.txt"], stdout=f) File "…/python3.10/subprocess.py", line 503, in run with Popen(*popenargs, **kwargs) as process: File "…/python3.10/subprocess.py", line 837, in __init__ errread, errwrite) = self._get_handles(stdin, stdout, stderr) File "…/python3.10/subprocess.py", line 1638, in _get_handles c2pwrite = stdout.fileno() io.UnsupportedOperation: fileno ``` An alternative is to use `check_output`, but I would like to do this without storing the subprocess output in memory since it may be large. ```py # This works but output is stored in memory output = check_output(["cat", "file1.txt"]) with xopen("file2.txt.xz", "wb") as f: f.write(output) ``` Questions: 1. Is there a way to achieve my goal with other subprocess functions/parameters? 2. If not, are there plans to support this in xopen?