Python subprocess check_call, native way to print STDERR if it fails?

Question

I often wish to perform the action of subprocess.check_output, i.e. print STDOUT live, and check the return code is 0 on exit. However if there is an error, I would like the STDERR to be printed. When looking at log files and just seeing the return code is often not very beneficial.

E.g.:

subprocess.check_call(['ping', '-c', '1', 'github.com2'])

Will generate this error:

subprocess.CalledProcessError: Command '['ping', '-c', '1', 'github.com2']' returned non-zero exit status 2.

Here we are left wondering why it failed, on real world examples it becomes critical to be able to see what the actual error is. So I find I always have to wrap such calls in something like this to be able to see STDERR:

import subprocess
cmds = ['ping', '-c', '1', 'github.com2']
result = subprocess.run(cmds, stderr=subprocess.PIPE)
if result.returncode != 0:
    msg = result.stderr.decode().strip()
    raise subprocess.CalledProcessError(f"CALLED SUBPROCESS ERROR: Command: {' '.join(cmds)}\nReturn code {result.returncode}\nSTDERR: {msg}\n")

With the above one gets to see that STDERR is:

ping: github.com2: Temporary failure in name resolution

I feel there must be a built in way using subprocess, but can't figure it out.

Im guessing it's not possible because CalledSubprocessError does not use STDERR is the string version of the exception:

class CalledProcessError(SubprocessError):
    """Raised when run() is called with check=True and the process
    returns a non-zero exit status.

    Attributes:
      cmd, returncode, stdout, stderr, output
    """
    def __init__(self, returncode, cmd, output=None, stderr=None):
        self.returncode = returncode
        self.cmd = cmd
        self.output = output
        self.stderr = stderr

    def __str__(self):
        if self.returncode and self.returncode < 0:
            try:
                return "Command '%s' died with %r." % (
                        self.cmd, signal.Signals(-self.returncode))
            except ValueError:
                return "Command '%s' died with unknown signal %d." % (
                        self.cmd, -self.returncode)
        else:
            return "Command '%s' returned non-zero exit status %d." % (
                    self.cmd, self.returncode)

    @property
    def stdout(self):
        """Alias for output attribute, to match stderr"""
        return self.output

    @stdout.setter
    def stdout(self, value):
        # There's no obvious reason to set this, but allow it anyway so
        # .stdout is a transparent alias for .output
        self.output = value

Answer 1

Calling subprocess.run(..., check=True) should provide all the needed info. From the manual: "If check is true, and the process exits with a non-zero exit code, a CalledProcessError exception will be raised. Attributes of that exception hold the arguments, the exit code, and stdout and stderr if they were captured."