Python2 compatibility

[lifeforms]

Hi, I maintain the FreeBSD port of grc and I'm busy updating our package to v1.11.

I noticed that the README states that grc has python2 + python3 compatibility.

The python3 in the shebang is not a problem, we replace that with the python interpreter of the user's choosing.

However, in commit 1516a3e the python3-only FileNotFoundError was introduced. This gives the following error on python2:

# grc foo
Traceback (most recent call last):
  File "/usr/local/bin/grc", line 193, in <module>
    except FileNotFoundError:
NameError: name 'FileNotFoundError' is not defined

Besides the try-except part, grc seems to still run fine on python2 otherwise.

I would like not forcing users to install python3, so I would prefer to change the try-except in grc to something like this, which would work in python2/3 and still be mostly informative I think:

        try:
            os.execvp(args[0], args)
        except OSError:
            sys.stderr.write('grc: %s: command not found\n' % args[0])
            sys.exit(1)
        except Exception as e:
            sys.stderr.write('grc: %s: %s\n' % (args[0], e.strerror))
            sys.exit(1)

Other solutions would be welcome too.

Alternatively, if grc will support python3 only, this doesn't need to be changed (but the README would); in that case I might either patch it downstream for python2 users or I would just require python3 as a dependency.

[garabik]

Good catch - I haven't noticed this while testing, because the nonexistent exception is invoked only if you run grc with an invalid command. I slightly modified your solution, since I prefer to have a full debug output if there is any other problem apart from OSError. I'll probably make a new fix-up release soon.

Yes, I'd very much prefer grc to work with python2 as well.