[Python] AttributeError: 'zstd.ZstdDecompressionReader' object has no attribute 'fileno'

I need to run a subprocess pipeline that uses zstandard files (too large to fit in memory) both as their input and output. Consider the following example:

import subprocess
import zstandard

with zstandard.open('a.txt.zst', 'w') as f:
f.write('hello\n')

f_in = zstandard.open('a.txt.zst', 'rb')
f_out = zstandard.open('b.txt.zst', 'wb')

# in reality I'd be running multiple programs here by chaining PIPEs, but first
# reads f_in and last writes to f_out:
subprocess.call(['cat'], stdin=f_in, stdout=f_out)


I'm getting the following error:

Traceback (most recent call last):
File "/tmp/a.py", line 12, in <module>
subprocess.call(['cat'], stdin=f_in, stdout=f_out)
File "/usr/lib/python3.11/subprocess.py", line 389, in call
with Popen(*popenargs, **kwargs) as p:
^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/subprocess.py", line 892, in __init__
errread, errwrite) = self._get_handles(stdin, stdout, stderr)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/subprocess.py", line 1661, in _get_handles
p2cread = stdin.fileno()
^^^^^^^^^^^^
AttributeError: 'zstd.ZstdDecompressionReader' object has no attribute 'fileno'


I'm thinking of using PIPEs at both ends and feeding them with threads, but it feels rather fragile. Is there a more idiomatic solution to this problem?

Continue reading...