Catch bash/git fatal in python

Question

I would like to write a simple python script which will be able to clone a git repository into desired directory. I used try...except construction to be able to catch all exceptions however it looks like I am not able to handle 'fatal' properly.

#!/usr/bin/env python
import subprocess

try:
    subprocess.check_call(['git', 'clone', 'git clone git@some_repo', '/tmp/some_directory'])
except Exception:
    print "There was a problem during repository configuration"

The output of the script above:

fatal: repository 'git clone git@some_repo' does not exist

There was a problem during repository configuration

To be more specific, I was rather expecting to get only the "There was a ..." message. Why do I get a 'fatal' message also?

Answer 1

You need to capture STDERR of your subprocess.check_call() execution. See Catch stderr in subprocess.check_call without using subprocess.PIPE

for details.

Answer 2

The message you are seeing is produced by the git command.

If you want to prevent that message from appearing you should redirect either standard error or all output to /dev/null through a shell, like:

subprocess.check_call(['git', 'clone', 'git clone git@some_repo', '/tmp/some_directory', '2&>/dev/null'], shell=True)

However, I'd recommend against that practice since you lose information on the actual cause of error.

Answer 3

As previously specified you need to capture the standard error. Also, as the documentation specifies, subprocess.check_call() just raises an exception when the return code is non-zero.

So, you could mimic the behavior as follows:

#!/usr/bin/env python
import subprocess

def clone_repository(): # customize your function parameters
    # prepare the arguments with your function parameters
    arguments = ['git', 'clone', 'git clone git@some_repo', '/tmp/some_directory']
    git_proc = subprocess.Popen(arguments)
    stdout, stderr = git_proc.communicate()
    if git_proc.returncode != 0:
        raise subprocess.CalledProcessError(arguments, git_proc.returncode)
    return stdout, stderr

try:
    stdout, stderr = clone_repository()
except (OSError, ValueError) as e:
    # this errors out when the arguments are invalid (ValueError)
    # or when there is an underlying file missing, etc (OSError)
    # put the print that you require for these errors
    pass 
except subprocess.CalledProcessError: 
    # you could use stderr to determine the underlying error
    print "There was a problem during repository configuration"