How to handle error when python's path is invalid?

[itsdax]

            const PythonShell = require('python-shell');
            const options = {
                pythonPath: './notthepythonpath',
                scriptPath: 'scriptdir',
                args: [0, 0, 400, 400, 1, store.get('outputPath')],
                mode: 'text',
            };
            let pyshell = new PythonShell('script.py', options);
            pyshell.on('error', (err) => {
                alert(err);
            });

I've tried the callback ,and tried on('error') but both doesn't seem to catch it.

[Almenon]

I'll have to look into that - the error event should fire for that.

Here's the code I use in arepl-vscode:

pyshell.childProcess.on('error', err => {
  let error:any = err; //typescript complains about type for some reason so defining to any
  this.pythonPreviewContentProvider.handleSpawnError(error.path, error.spawnargs[0], error.stack);
})

[sejsingffdc]

I ran into the same problem. I believe the root cause is with this line in python-shell:

this.childProcess = child_process_1.spawn(pythonPath, this.command, options);

the spawn() function can throw an exception if the path is invalid (see here nwjs/nw.js#1623). It appears that spawn must have an error handler attached like this:

spawn.on('error', function (err) {
    console.log('spawn error:', err);
});

[sejsingffdc]

This code is in PythonShell's constructor.

According to the docs at https://nodejs.org/api/child_process.html#child_process_child_process_spawn_command_args_options, the error handler should be set on the spawned subprocess itself, not on spawn:

Example of checking for failed spawn:

const { spawn } = require('child_process');
const subprocess = spawn('bad_command');

subprocess.on('error', (err) => {
  console.log('Failed to start subprocess.');
});

Just to be sure I just checked:

Node.js> child_process.spawn.on
undefined

[sejsingffdc]

Could it be OS dependent behavior? I'm on Mac.

[Almenon]

@sejsingffdc nah, I have windows and it does same thing.

I'll change the error event to also fire when the path is invalid.

Once I finish promise support (#77) the python process will be launched via a start method which will return or reject a promise based on whether it sucessfully launched the process.