How to use a custom file-like object as subprocess stdout/stderr?
python, subprocess
Solution
According to the documentation:
stdin, stdout and stderr specify the executed program’s standard input, standard output and standard error file handles, respectively. Valid values are PIPE, DEVNULL, an existing file descriptor (a positive integer), an existing file object, and None.
Using `subprocess.PIPE`:
proc = subprocess.Popen(['bash', '-c', 'echo Testing'],
stdout=subprocess.PIPE,
stderr=subprocess.STDOUT)
print('Writing:', proc.stdout.read())
# OR print('Writing:', proc.stdout.read().decode())
Problem
Consider this code, where a `subprocess.Popen` is spawned. I'd like writes to the subprocess' `stdout` and `stderr` to go to my custom file-object's `.write()` method, however this isn't the case. ``` import subprocess class Printer: def __init__(self): pass def write(self, chunk): print('Writing:', chunk) def fileno(self): return 0 def close(self): return proc = subprocess.Popen(['bash', '-c', 'echo Testing'], stdout=Printer(), stderr=subprocess.STDOUT) proc.wait() ``` Why is the `.write()` method not used, and what is the use of specifying a `stdout=` parameter in this case?